diff --git a/docs/examples/validators_root.py b/docs/examples/validators_root.py
new file mode 100644
--- /dev/null
+++ b/docs/examples/validators_root.py
@@ -0,0 +1,41 @@
+from pydantic import BaseModel, ValidationError, root_validator
+
+class UserModel(BaseModel):
+    username: str
+    password1: str
+    password2: str
+
+    @root_validator(pre=True)
+    def check_card_number_omitted(cls, values):
+        assert 'card_number' not in values, 'card_number should not be included'
+        return values
+
+    @root_validator
+    def check_passwords_match(cls, values):
+        pw1, pw2 = values.get('password1'), values.get('password2')
+        if pw1 is not None and pw2 is not None and pw1 != pw2:
+            raise ValueError('passwords do not match')
+        return values
+
+print(UserModel(username='scolvin', password1='zxcvbn', password2='zxcvbn'))
+#> UserModel username='scolvin' password1='zxcvbn' password2='zxcvbn'
+
+try:
+    UserModel(username='scolvin', password1='zxcvbn', password2='zxcvbn2')
+except ValidationError as e:
+    print(e)
+"""
+1 validation error for UserModel
+__root__
+  passwords do not match (type=value_error)
+"""
+
+try:
+    UserModel(username='scolvin', password1='zxcvbn', password2='zxcvbn', card_number='1234')
+except ValidationError as e:
+    print(e)
+"""
+1 validation error for UserModel
+__root__
+  card_number should not be included (type=assertion_error)
+"""
diff --git a/docs/examples/validators_simple.py b/docs/examples/validators_simple.py
--- a/docs/examples/validators_simple.py
+++ b/docs/examples/validators_simple.py
@@ -1,6 +1,5 @@
 from pydantic import BaseModel, ValidationError, validator
 
-
 class UserModel(BaseModel):
     name: str
     username: str
@@ -24,16 +23,15 @@ def username_alphanumeric(cls, v):
         assert v.isalpha(), 'must be alphanumeric'
         return v
 
-
 print(UserModel(name='samuel colvin', username='scolvin', password1='zxcvbn', password2='zxcvbn'))
-# > UserModel name='Samuel Colvin' password1='zxcvbn' password2='zxcvbn'
+#> UserModel name='Samuel Colvin' username='scolvin' password1='zxcvbn' password2='zxcvbn'
 
 try:
     UserModel(name='samuel', username='scolvin', password1='zxcvbn', password2='zxcvbn2')
 except ValidationError as e:
     print(e)
 """
-2 validation errors
+2 validation errors for UserModel
 name
   must contain a space (type=value_error)
 password2
diff --git a/pydantic/__init__.py b/pydantic/__init__.py
--- a/pydantic/__init__.py
+++ b/pydantic/__init__.py
@@ -1,6 +1,6 @@
 # flake8: noqa
 from . import dataclasses
-from .class_validators import validator
+from .class_validators import root_validator, validator
 from .env_settings import BaseSettings
 from .error_wrappers import ValidationError
 from .errors import *
diff --git a/pydantic/class_validators.py b/pydantic/class_validators.py
--- a/pydantic/class_validators.py
+++ b/pydantic/class_validators.py
@@ -4,24 +4,24 @@
 from inspect import Signature, signature
 from itertools import chain
 from types import FunctionType
-from typing import TYPE_CHECKING, Any, Callable, Dict, List, Optional, Set, Type
+from typing import TYPE_CHECKING, Any, Callable, Dict, Iterable, List, Optional, Set, Tuple, Type, Union
 
 from .errors import ConfigError
 from .typing import AnyCallable
 from .utils import in_ipython
 
-if TYPE_CHECKING:  # pragma: no cover
-    from .main import BaseConfig
-    from .fields import Field
-    from .types import ModelOrDc
-
-    ValidatorCallable = Callable[[Optional[ModelOrDc], Any, Dict[str, Any], Field, Type[BaseConfig]], Any]
-
 
 class Validator:
     __slots__ = 'func', 'pre', 'each_item', 'always', 'check_fields'
 
-    def __init__(self, func: AnyCallable, pre: bool, each_item: bool, always: bool, check_fields: bool):
+    def __init__(
+        self,
+        func: AnyCallable,
+        pre: bool = False,
+        each_item: bool = False,
+        always: bool = False,
+        check_fields: bool = False,
+    ):
         self.func = func
         self.pre = pre
         self.each_item = each_item
@@ -29,7 +29,19 @@ def __init__(self, func: AnyCallable, pre: bool, each_item: bool, always: bool,
         self.check_fields = check_fields
 
 
+if TYPE_CHECKING:  # pragma: no cover
+    from .main import BaseConfig
+    from .fields import Field
+    from .types import ModelOrDc
+
+    ValidatorCallable = Callable[[Optional[ModelOrDc], Any, Dict[str, Any], Field, Type[BaseConfig]], Any]
+    ValidatorsList = List[ValidatorCallable]
+    ValidatorListDict = Dict[str, List[Validator]]
+
 _FUNCS: Set[str] = set()
+ROOT_KEY = '__root__'
+VALIDATOR_CONFIG_KEY = '__validator_config__'
+ROOT_VALIDATOR_CONFIG_KEY = '__root_validator_config__'
 
 
 def validator(
@@ -66,39 +78,62 @@ def validator(
         each_item = not whole
 
     def dec(f: AnyCallable) -> classmethod:
-        # avoid validators with duplicated names since without this validators can be overwritten silently
-        # which generally isn't the intended behaviour, don't run in ipython - see #312
-        if not in_ipython():  # pragma: no branch
-            ref = f.__module__ + '.' + f.__qualname__
-            if ref in _FUNCS:
-                raise ConfigError(f'duplicate validator function "{ref}"')
-            _FUNCS.add(ref)
+        _check_validator_name(f)
         f_cls = classmethod(f)
-        f_cls.__validator_config = (  # type: ignore
-            fields,
-            Validator(func=f, pre=pre, each_item=each_item, always=always, check_fields=check_fields),
+        setattr(
+            f_cls,
+            VALIDATOR_CONFIG_KEY,
+            (fields, Validator(func=f, pre=pre, each_item=each_item, always=always, check_fields=check_fields)),
         )
         return f_cls
 
     return dec
 
 
-ValidatorListDict = Dict[str, List[Validator]]
+def root_validator(
+    _func: Optional[AnyCallable] = None, *, pre: bool = False
+) -> Union[classmethod, Callable[[AnyCallable], classmethod]]:
+    if _func:
+        _check_validator_name(_func)
+        f_cls = classmethod(_func)
+        setattr(f_cls, ROOT_VALIDATOR_CONFIG_KEY, Validator(func=_func, pre=pre))
+        return f_cls
+
+    def dec(f: AnyCallable) -> classmethod:
+        _check_validator_name(f)
+        f_cls = classmethod(f)
+        setattr(f_cls, ROOT_VALIDATOR_CONFIG_KEY, Validator(func=f, pre=pre))
+        return f_cls
+
+    return dec
+
+
+def _check_validator_name(f: AnyCallable) -> None:
+    """
+    avoid validators with duplicated names since without this, validators can be overwritten silently
+    which generally isn't the intended behaviour, don't run in ipython - see #312
+    """
+    if not in_ipython():  # pragma: no branch
+        ref = f.__module__ + '.' + f.__qualname__
+        if ref in _FUNCS:
+            raise ConfigError(f'duplicate validator function "{ref}"')
+        _FUNCS.add(ref)
 
 
 class ValidatorGroup:
-    def __init__(self, validators: ValidatorListDict) -> None:
+    def __init__(self, validators: 'ValidatorListDict') -> None:
         self.validators = validators
         self.used_validators = {'*'}
 
     def get_validators(self, name: str) -> Optional[Dict[str, Validator]]:
         self.used_validators.add(name)
-        specific_validators = self.validators.get(name)
-        wildcard_validators = self.validators.get('*')
-        if specific_validators or wildcard_validators:
-            validators = (specific_validators or []) + (wildcard_validators or [])
+        validators = self.validators.get(name, [])
+        if name != ROOT_KEY:
+            validators += self.validators.get('*', [])
+        if validators:
             return {v.func.__name__: v for v in validators}
-        return None
+        else:
+            return None
 
     def check_for_unused(self) -> None:
         unused_validators = set(
@@ -120,7 +155,7 @@ def check_for_unused(self) -> None:
 def extract_validators(namespace: Dict[str, Any]) -> Dict[str, List[Validator]]:
     validators: Dict[str, List[Validator]] = {}
     for var_name, value in namespace.items():
-        validator_config = getattr(value, '__validator_config', None)
+        validator_config = getattr(value, VALIDATOR_CONFIG_KEY, None)
         if validator_config:
             fields, v = validator_config
             for field in fields:
@@ -131,7 +166,30 @@ def extract_validators(namespace: Dict[str, Any]) -> Dict[str, List[Validator]]:
     return validators
 
 
-def inherit_validators(base_validators: ValidatorListDict, validators: ValidatorListDict) -> ValidatorListDict:
+def extract_root_validators(namespace: Dict[str, Any]) -> Tuple[List[AnyCallable], List[AnyCallable]]:
+    pre_validators: List[AnyCallable] = []
+    post_validators: List[AnyCallable] = []
+    for name, value in namespace.items():
+        validator_config: Optional[Validator] = getattr(value, ROOT_VALIDATOR_CONFIG_KEY, None)
+        if validator_config:
+            sig = signature(validator_config.func)
+            args = list(sig.parameters.keys())
+            if args[0] == 'self':
+                raise ConfigError(
+                    f'Invalid signature for root validator {name}: {sig}, "self" not permitted as first argument, '
+                    f'should be: (cls, values).'
+                )
+            if len(args) != 2:
+                raise ConfigError(f'Invalid signature for root validator {name}: {sig}, should be: (cls, values).')
+            # check function signature
+            if validator_config.pre:
+                pre_validators.append(validator_config.func)
+            else:
+                post_validators.append(validator_config.func)
+    return pre_validators, post_validators
+
+
+def inherit_validators(base_validators: 'ValidatorListDict', validators: 'ValidatorListDict') -> 'ValidatorListDict':
     for field, field_validators in base_validators.items():
         if field not in validators:
             validators[field] = []
@@ -165,6 +223,10 @@ def make_generic_validator(validator: AnyCallable) -> 'ValidatorCallable':
         return wraps(validator)(_generic_validator_basic(validator, sig, set(args)))
 
 
+def prep_validators(v_funcs: Iterable[AnyCallable]) -> 'ValidatorsList':
+    return [make_generic_validator(f) for f in v_funcs if f]
+
+
 all_kwargs = {'values', 'field', 'config'}
 
 
@@ -235,6 +297,10 @@ def _generic_validator_basic(validator: AnyCallable, sig: Signature, args: Set[s
         return lambda cls, v, values, field, config: validator(v, values=values, field=field, config=config)
 
 
-def gather_validators(type_: 'ModelOrDc') -> Dict[str, classmethod]:
+def gather_all_validators(type_: 'ModelOrDc') -> Dict[str, classmethod]:
     all_attributes = ChainMap(*[cls.__dict__ for cls in type_.__mro__])
-    return {k: v for k, v in all_attributes.items() if hasattr(v, '__validator_config')}
+    return {
+        k: v
+        for k, v in all_attributes.items()
+        if hasattr(v, VALIDATOR_CONFIG_KEY) or hasattr(v, ROOT_VALIDATOR_CONFIG_KEY)
+    }
diff --git a/pydantic/dataclasses.py b/pydantic/dataclasses.py
--- a/pydantic/dataclasses.py
+++ b/pydantic/dataclasses.py
@@ -1,7 +1,7 @@
 import dataclasses
 from typing import TYPE_CHECKING, Any, Callable, Dict, Generator, Optional, Type, Union
 
-from .class_validators import gather_validators
+from .class_validators import gather_all_validators
 from .error_wrappers import ValidationError
 from .errors import DataclassTypeError
 from .fields import Required
@@ -67,7 +67,9 @@ def _process_class(
     def _pydantic_post_init(self: 'DataclassType', *initvars: Any) -> None:
         if post_init_original is not None:
             post_init_original(self, *initvars)
-        d = validate_model(self.__pydantic_model__, self.__dict__, cls=self.__class__)[0]
+        d, _, validation_error = validate_model(self.__pydantic_model__, self.__dict__, cls=self.__class__)
+        if validation_error:
+            raise validation_error
         object.__setattr__(self, '__dict__', d)
         object.__setattr__(self, '__initialised__', True)
         if post_init_post_parse is not None:
@@ -81,7 +83,7 @@ def _pydantic_post_init(self: 'DataclassType', *initvars: Any) -> None:
         for field in dataclasses.fields(cls)
     }
 
-    validators = gather_validators(cls)
+    validators = gather_all_validators(cls)
     cls.__pydantic_model__ = create_model(
         cls.__name__, __config__=config, __module__=_cls.__module__, __validators__=validators, **fields
     )
diff --git a/pydantic/fields.py b/pydantic/fields.py
--- a/pydantic/fields.py
+++ b/pydantic/fields.py
@@ -4,7 +4,6 @@
     Dict,
     FrozenSet,
     Generator,
-    Iterable,
     Iterator,
     List,
     Mapping,
@@ -19,11 +18,11 @@
 )
 
 from . import errors as errors_
-from .class_validators import Validator, make_generic_validator
+from .class_validators import Validator, make_generic_validator, prep_validators
 from .error_wrappers import ErrorWrapper
 from .errors import NoneIsNotAllowedError
 from .types import Json, JsonWrapper
-from .typing import AnyCallable, AnyType, Callable, ForwardRef, display_as_type, is_literal_type, literal_values
+from .typing import AnyType, Callable, ForwardRef, display_as_type, is_literal_type, literal_values
 from .utils import lenient_issubclass, sequence_like
 from .validators import constant_validator, dict_validator, find_validators, validate_json
 
@@ -36,13 +35,12 @@
 NoneType = type(None)
 
 if TYPE_CHECKING:  # pragma: no cover
-    from .class_validators import ValidatorCallable  # noqa: F401
+    from .class_validators import ValidatorsList  # noqa: F401
     from .error_wrappers import ErrorList
     from .main import BaseConfig, BaseModel  # noqa: F401
     from .schema import Schema  # noqa: F401
     from .types import ModelOrDc  # noqa: F401
 
-    ValidatorsList = List[ValidatorCallable]
     ValidateReturn = Tuple[Optional[Any], Optional[ErrorList]]
     LocStr = Union[Tuple[Union[int, str], ...], str]
 
@@ -238,7 +236,7 @@ def _type_analysis(self) -> None:  # noqa: C901 (ignore complexity)
             if get_validators:
                 self.class_validators.update(
                     {
-                        f'list_{i}': Validator(validator, each_item=False, pre=True, always=True, check_fields=False)
+                        f'list_{i}': Validator(validator, pre=True, always=True)
                         for i, validator in enumerate(get_validators())
                     }
                 )
@@ -285,7 +283,7 @@ def _populate_validators(self) -> None:
                 *(get_validators() if get_validators else list(find_validators(self.type_, self.model_config))),
                 *[v.func for v in class_validators_ if v.each_item and not v.pre],
             )
-            self.validators = self._prep_vals(v_funcs)
+            self.validators = prep_validators(v_funcs)
 
         # Add const validator
         self.pre_validators = []
@@ -294,8 +292,8 @@ def _populate_validators(self) -> None:
             self.pre_validators = [make_generic_validator(constant_validator)]
 
         if class_validators_:
-            self.pre_validators += self._prep_vals(v.func for v in class_validators_ if not v.each_item and v.pre)
-            self.post_validators = self._prep_vals(v.func for v in class_validators_ if not v.each_item and not v.pre)
+            self.pre_validators += prep_validators(v.func for v in class_validators_ if not v.each_item and v.pre)
+            self.post_validators = prep_validators(v.func for v in class_validators_ if not v.each_item and not v.pre)
 
         if self.parse_json:
             self.pre_validators.append(make_generic_validator(validate_json))
@@ -303,10 +301,6 @@ def _populate_validators(self) -> None:
         self.pre_validators = self.pre_validators or None
         self.post_validators = self.post_validators or None
 
-    @staticmethod
-    def _prep_vals(v_funcs: Iterable[AnyCallable]) -> 'ValidatorsList':
-        return [make_generic_validator(f) for f in v_funcs if f]
-
     def validate(
         self, v: Any, values: Dict[str, Any], *, loc: 'LocStr', cls: Optional['ModelOrDc'] = None
     ) -> 'ValidateReturn':
diff --git a/pydantic/generics.py b/pydantic/generics.py
--- a/pydantic/generics.py
+++ b/pydantic/generics.py
@@ -1,7 +1,7 @@
 from typing import Any, ClassVar, Dict, Generic, Tuple, Type, TypeVar, Union, get_type_hints
 
-from pydantic.class_validators import gather_validators
-from pydantic.main import BaseModel, create_model
+from .class_validators import gather_all_validators
+from .main import BaseModel, create_model
 
 _generic_types_cache: Dict[Tuple[Type[Any], Union[Any, Tuple[Any, ...]]], Type[BaseModel]] = {}
 GenericModelT = TypeVar('GenericModelT', bound='GenericModel')
@@ -41,7 +41,7 @@ def __class_getitem__(  # type: ignore
         }
 
         model_name = concrete_name(cls, params)
-        validators = gather_validators(cls)
+        validators = gather_all_validators(cls)
         fields: Dict[str, Tuple[Type[Any], Any]] = {
             k: (v, cls.__fields__[k].default) for k, v in concrete_type_hints.items() if k in cls.__fields__
         }
diff --git a/pydantic/main.py b/pydantic/main.py
--- a/pydantic/main.py
+++ b/pydantic/main.py
@@ -7,9 +7,9 @@
 from functools import partial
 from pathlib import Path
 from types import FunctionType
-from typing import TYPE_CHECKING, Any, Callable, Dict, Optional, Tuple, Type, TypeVar, Union, cast, no_type_check
+from typing import TYPE_CHECKING, Any, Callable, Dict, List, Optional, Tuple, Type, TypeVar, Union, cast, no_type_check
 
-from .class_validators import ValidatorGroup, extract_validators, inherit_validators
+from .class_validators import ROOT_KEY, ValidatorGroup, extract_root_validators, extract_validators, inherit_validators
 from .error_wrappers import ErrorWrapper, ValidationError
 from .errors import ConfigError, DictError, ExtraError, MissingError
 from .fields import SHAPE_MAPPING, Field
@@ -64,6 +64,7 @@ class BaseConfig:
     error_msg_templates: Dict[str, str] = {}
     arbitrary_types_allowed = False
     orm_mode: bool = False
+    getter_dict: Type[GetterDict] = GetterDict
     alias_generator: Optional[Callable[[str], str]] = None
     keep_untouched: Tuple[type, ...] = ()
     schema_extra: Dict[str, Any] = {}
@@ -108,13 +109,13 @@ def set_extra(config: Type[BaseConfig], cls_name: str) -> None:
 def is_valid_field(name: str) -> bool:
     if not name.startswith('_'):
         return True
-    return '__root__' == name
+    return ROOT_KEY == name
 
 
 def validate_custom_root_type(fields: Dict[str, Field]) -> None:
     if len(fields) > 1:
         raise ValueError('__root__ cannot be mixed with other fields')
-    if fields['__root__'].shape == SHAPE_MAPPING:
+    if fields[ROOT_KEY].shape == SHAPE_MAPPING:
         raise TypeError('custom root type cannot allow mapping')
 
 
@@ -127,11 +128,14 @@ def __new__(mcs, name, bases, namespace):
         fields: Dict[str, Field] = {}
         config = BaseConfig
         validators: 'ValidatorListDict' = {}
+        pre_root_validators, post_root_validators = [], []
         for base in reversed(bases):
             if issubclass(base, BaseModel) and base != BaseModel:
                 fields.update(deepcopy(base.__fields__))
                 config = inherit_config(base.__config__, config)
                 validators = inherit_validators(base.__validators__, validators)
+                pre_root_validators += base.__pre_root_validators__
+                post_root_validators += base.__post_root_validators__
 
         config = inherit_config(namespace.get('Config'), config)
         validators = inherit_validators(extract_validators(namespace), validators)
@@ -190,7 +194,7 @@ def __new__(mcs, name, bases, namespace):
                         )
                     fields[var_name] = inferred
 
-        _custom_root_type = '__root__' in fields
+        _custom_root_type = ROOT_KEY in fields
         if _custom_root_type:
             validate_custom_root_type(fields)
         vg.check_for_unused()
@@ -198,10 +202,13 @@ def __new__(mcs, name, bases, namespace):
             json_encoder = partial(custom_pydantic_encoder, config.json_encoders)
         else:
             json_encoder = pydantic_encoder
+        pre_rv_new, post_rv_new = extract_root_validators(namespace)
         new_namespace = {
             '__config__': config,
             '__fields__': fields,
             '__validators__': vg.validators,
+            '__pre_root_validators__': pre_root_validators + pre_rv_new,
+            '__post_root_validators__': post_root_validators + post_rv_new,
             '_schema_cache': {},
             '_json_encoder': staticmethod(json_encoder),
             '_custom_root_type': _custom_root_type,
@@ -215,6 +222,8 @@ class BaseModel(metaclass=MetaModel):
         # populated by the metaclass, defined here to help IDEs only
         __fields__: Dict[str, Field] = {}
         __validators__: Dict[str, AnyCallable] = {}
+        __pre_root_validators__: List[AnyCallable]
+        __post_root_validators__: List[AnyCallable]
         __config__: Type[BaseConfig] = BaseConfig
         __root__: Any = None
         _json_encoder: Callable[[Any], Any] = lambda x: x
@@ -229,7 +238,9 @@ def __init__(__pydantic_self__, **data: Any) -> None:
         if TYPE_CHECKING:  # pragma: no cover
             __pydantic_self__.__dict__: Dict[str, Any] = {}
             __pydantic_self__.__fields_set__: 'SetStr' = set()
-        values, fields_set, _ = validate_model(__pydantic_self__, data)
+        values, fields_set, validation_error = validate_model(__pydantic_self__.__class__, data)
+        if validation_error:
+            raise validation_error
         object.__setattr__(__pydantic_self__, '__dict__', values)
         object.__setattr__(__pydantic_self__, '__fields_set__', fields_set)
 
@@ -308,20 +319,20 @@ def json(
         encoder = cast(Callable[[Any], Any], encoder or self._json_encoder)
         data = self.dict(include=include, exclude=exclude, by_alias=by_alias, skip_defaults=skip_defaults)
         if self._custom_root_type:
-            data = data['__root__']
+            data = data[ROOT_KEY]
         return self.__config__.json_dumps(data, default=encoder, **dumps_kwargs)
 
     @classmethod
     def parse_obj(cls: Type['Model'], obj: Any) -> 'Model':
         if not isinstance(obj, dict):
             if cls._custom_root_type:
-                obj = {'__root__': obj}
+                obj = {ROOT_KEY: obj}
             else:
                 try:
                     obj = dict(obj)
                 except (TypeError, ValueError) as e:
                     exc = TypeError(f'{cls.__name__} expected dict not {type(obj).__name__}')
-                    raise ValidationError([ErrorWrapper(exc, loc='__obj__')], cls) from e
+                    raise ValidationError([ErrorWrapper(exc, loc=ROOT_KEY)], cls) from e
         return cls(**obj)
 
     @classmethod
@@ -344,7 +355,7 @@ def parse_raw(
                 json_loads=cls.__config__.json_loads,
             )
         except (ValueError, TypeError, UnicodeDecodeError) as e:
-            raise ValidationError([ErrorWrapper(e, loc='__obj__')], cls)
+            raise ValidationError([ErrorWrapper(e, loc=ROOT_KEY)], cls)
         return cls.parse_obj(obj)
 
     @classmethod
@@ -366,7 +377,9 @@ def from_orm(cls: Type['Model'], obj: Any) -> 'Model':
             raise ConfigError('You must have the config attribute orm_mode=True to use from_orm')
         obj = cls._decompose_class(obj)
         m = cls.__new__(cls)
-        values, fields_set, _ = validate_model(m, obj)
+        values, fields_set, validation_error = validate_model(cls, obj)
+        if validation_error:
+            raise validation_error
         object.__setattr__(m, '__dict__', values)
         object.__setattr__(m, '__fields_set__', fields_set)
         return m
@@ -467,7 +480,7 @@ def validate(cls: Type['Model'], value: Any) -> 'Model':
 
     @classmethod
     def _decompose_class(cls: Type['Model'], obj: Any) -> GetterDict:
-        return GetterDict(obj)
+        return cls.__config__.getter_dict(obj)
 
     @classmethod
     @no_type_check
@@ -681,7 +694,7 @@ def create_model(
 
 
 def validate_model(  # noqa: C901 (ignore complexity)
-    model: Union[BaseModel, Type[BaseModel]], input_data: 'DictStrAny', raise_exc: bool = True, cls: 'ModelOrDc' = None
+    model: Type[BaseModel], input_data: 'DictStrAny', cls: 'ModelOrDc' = None
 ) -> Tuple['DictStrAny', 'SetStr', Optional[ValidationError]]:
     """
     validate data against a model.
@@ -694,7 +707,13 @@ def validate_model(  # noqa: C901 (ignore complexity)
     fields_set = set()
     config = model.__config__
     check_extra = config.extra is not Extra.ignore
-    cls_ = cls or model.__class__
+    cls_ = cls or model
+
+    for validator in model.__pre_root_validators__:
+        try:
+            input_data = validator(cls_, input_data)
+        except (ValueError, TypeError, AssertionError) as exc:
+            return {}, set(), ValidationError([ErrorWrapper(exc, loc=ROOT_KEY)], cls_)
 
     for name, field in model.__fields__.items():
         if type(field.type_) == ForwardRef:
@@ -728,7 +747,7 @@ def validate_model(  # noqa: C901 (ignore complexity)
             if check_extra:
                 names_used.add(field.name if using_name else field.alias)
 
-        v_, errors_ = field.validate(value, values, loc=field.alias, cls=cls_)  # type: ignore
+        v_, errors_ = field.validate(value, values, loc=field.alias, cls=cls_)
         if isinstance(errors_, ErrorWrapper):
             errors.append(errors_)
         elif isinstance(errors_, list):
@@ -737,7 +756,10 @@ def validate_model(  # noqa: C901 (ignore complexity)
             values[name] = v_
 
     if check_extra:
-        extra = input_data.keys() - names_used
+        if isinstance(input_data, GetterDict):
+            extra = input_data.extra_keys() - names_used
+        else:
+            extra = input_data.keys() - names_used
         if extra:
             fields_set |= extra
             if config.extra is Extra.allow:
@@ -747,15 +769,14 @@ def validate_model(  # noqa: C901 (ignore complexity)
                 for f in sorted(extra):
                     errors.append(ErrorWrapper(ExtraError(), loc=f))
 
-    err = None
-    if errors:
-        model_type = model if isinstance(model, type) else type(model)
-        err = ValidationError(errors, model_type)
-
-    if not raise_exc:
-        return values, fields_set, err
-
-    if err:
-        raise err
+    for validator in model.__post_root_validators__:
+        try:
+            values = validator(cls_, values)
+        except (ValueError, TypeError, AssertionError) as exc:
+            errors.append(ErrorWrapper(exc, loc=ROOT_KEY))
+            break
 
-    return values, fields_set, None
+    if errors:
+        return values, fields_set, ValidationError(errors, cls_)
+    else:
+        return values, fields_set, None
diff --git a/pydantic/schema.py b/pydantic/schema.py
--- a/pydantic/schema.py
+++ b/pydantic/schema.py
@@ -11,6 +11,7 @@
 
 from pydantic.color import Color
 
+from .class_validators import ROOT_KEY
 from .fields import SHAPE_LIST, SHAPE_MAPPING, SHAPE_SET, SHAPE_SINGLETON, SHAPE_TUPLE, Field
 from .json import pydantic_encoder
 from .networks import AnyUrl, EmailStr, IPvAnyAddress, IPvAnyInterface, IPvAnyNetwork, NameEmail
@@ -586,8 +587,8 @@ def model_type_schema(
             properties[k] = f_schema
             if f.required:
                 required.append(k)
-    if '__root__' in properties:
-        out_schema = properties['__root__']
+    if ROOT_KEY in properties:
+        out_schema = properties[ROOT_KEY]
         out_schema['title'] = model.__config__.title or model.__name__
     else:
         out_schema = {'type': 'object', 'properties': properties}
diff --git a/pydantic/types.py b/pydantic/types.py
--- a/pydantic/types.py
+++ b/pydantic/types.py
@@ -26,11 +26,6 @@
     strict_str_validator,
 )
 
-try:
-    import email_validator
-except ImportError:
-    email_validator = None
-
 __all__ = [
     'NoneStr',
     'NoneBytes',
diff --git a/pydantic/utils.py b/pydantic/utils.py
--- a/pydantic/utils.py
+++ b/pydantic/utils.py
@@ -1,8 +1,8 @@
 import inspect
 from importlib import import_module
-from typing import TYPE_CHECKING, Any, List, Optional, Set, Tuple, Type, Union, no_type_check
+from typing import TYPE_CHECKING, Any, Iterator, List, Optional, Set, Tuple, Type, Union, no_type_check
 
-from .typing import AnyType
+from .typing import AnyType, display_as_type
 
 try:
     from typing_extensions import Literal
@@ -93,6 +93,8 @@ def almost_equal_floats(value_1: float, value_2: float, *, delta: float = 1e-8)
 class GetterDict:
     """
     Hack to make object's smell just enough like dicts for validate_model.
+
+    We can't inherit from Mapping[str, Any] because it upsets cython so we have to implement all methods ourselves.
     """
 
     __slots__ = ('_obj',)
@@ -100,15 +102,52 @@ class GetterDict:
     def __init__(self, obj: Any):
         self._obj = obj
 
-    def get(self, item: Any, default: Any) -> Any:
-        return getattr(self._obj, item, default)
+    def __getitem__(self, key: str) -> Any:
+        try:
+            return getattr(self._obj, key)
+        except AttributeError as e:
+            raise KeyError(key) from e
+
+    def get(self, key: Any, default: Any = None) -> Any:
+        return getattr(self._obj, key, default)
 
-    def keys(self) -> Set[Any]:
+    def extra_keys(self) -> Set[Any]:
         """
         We don't want to get any other attributes of obj if the model didn't explicitly ask for them
         """
         return set()
 
+    def keys(self) -> List[Any]:
+        """
+        Keys of the pseudo dictionary, uses a list not set so order information can be maintained like python
+        dictionaries.
+        """
+        return list(self)
+
+    def values(self) -> List[Any]:
+        return [self[k] for k in self]
+
+    def items(self) -> Iterator[Tuple[str, Any]]:
+        for k in self:
+            yield k, self.get(k)
+
+    def __iter__(self) -> Iterator[str]:
+        for name in dir(self._obj):
+            if not name.startswith('_'):
+                yield name
+
+    def __len__(self) -> int:
+        return sum(1 for _ in self)
+
+    def __contains__(self, item: Any) -> bool:
+        return item in self.keys()
+
+    def __eq__(self, other: Any) -> bool:
+        return dict(self) == dict(other.items())  # type: ignore
+
+    def __repr__(self) -> str:
+        return f'<GetterDict({display_as_type(self._obj)}) {dict(self)}>'  # type: ignore
+
 
 class ValueItems:
     """

It seems so good to me.

> We should change this in v1 to `__root__` to better match other nomenclature, eg. custom root types, where we use `__root__`.

I know about custom root type.  But, someone might not understand the `__root__` clearly.
agreed, documentation will need improving, but better to use one term everywhere.

I'm not wedded to the term "root" other offers considered...
I agree.

My answer is `__root__` for the title of the issue. 

> We should also implement at some point entire model validation

For the sake of discussion, here's a somewhat radical proposal:
1. If the list of fields passed to the validator is empty, it becomes a `__root__`/entire-model validator (depending on whether the model has a non-default `__root__`). (I see no reason to drop support for `@validator('__root__')`, but wouldn't be opposed to it for simplicity's sake.)
2. The `loc` field of `ErrorWrapper` is changed from typically containing `{field.name}` to typically containing`{Model.Config.title or Model.__name__}.{field.name}`.
    * I recognize that right now, validation happens inside the `Field`, which is not aware of the containing model. I think this could be addressed by the existence of a function/method that returns a modified `ErrorWrapper` where `loc` includes the name of the model.
3. For `__root__` or entire-model validation, drop the `.{field.name}` from `loc`.

Technical implementation challenges aside, I think this might be a good way to achieve a unified interface for specifying whole-model *and* `__root__` validators, and for achieving consistent error labeling.

I'll open a separate issue to discuss the implications of adding the model name to `ErrorWrapper`, but, any thoughts on this in the context of handling root errors?
So you're basically suggesting prefixing `loc` with the model name?

The problem is that very often (in few types of case, but the large majority of cases) we're simply doing something like:

```py
class LoginModel:
    email: EmailStr
    password: constr(max_length=100)

def login_view(request):
  m = LoginModel(**request.json())
  ...
```
The user (or frontend developer) has never heard of `LoginModel`, so an error at `loc: ['LoginModel', 'email']` is a lot more confusing than at `loc: ['email']`.

We could just use the model name instead of `__root__` for those errors?
I know that in theory `loc` is designed to be processed by the middleware of using package and used to generate the final error format, but I for one quite often end up using it directly.
@samuelcolvin I was coming from the context of FastAPI, and was imagining that the model name is externally available through the OpenAPI spec. But maybe that is a big assumption (especially if you want validation errors but don't want a public OpenAPI spec). I guess it would be nice if there were a config setting for `include_model_name_in_error_loc` (or something less verbose 😅). That would make it possible to optionally incorporate the change without many changes to code, and without needing to worry about causing conflicts with frameworks using pydantic (like FastAPI).

Either way, I think `__root__` would be similarly confusing externally. But it would have the advantage of leaking less implementation information if you wanted to avoid that.
I agree `__root__` isn't much better. But at least it won't get added to the majority of errors which have a field.

What do others think?

Also what do other libraries do? Django (and presumably therefore DRF) uses `__all__` which is no clearer than `__root__`.
I've thought this through some more, and given ValidationError tracebacks now include the model name, I think it makes sense to just use `__root__` everywhere (and prefer this to `__all__`). For the sake of debugging, I think it's fine to require access to the tracebacks to determine the model name. I'll take a shot at implementing.
@samuelcolvin I tried taking a shot at this, but I think I got in over my head. Validation currently always happens in a field, and I couldn't find a way to add "root" validation for non-custom-root models without substantial and/or very-likely-controversial changes. Given the amount of changes that it seemed like I'd have to make, (not to mention the effort required to get it to actually *work* even if I *was* willing to make large changes), I'm going to leave this to you for now.

(If you have an approach in mind that you think should work, I would also be happy to put in some renewed effort given more guidance.)
@dmontagu do you have your unfinished code in a fork or branch somewhere where I can take a look at it?
@skewty I'll look, but I'd probably advise against basing anything off of it, as I made a number of choices that backed me into a corner that I don't think had any hope of success. And I *suspect* any approach to this will have to get pretty deep into the internals, so it's probably better not to push your thinking down the same line that led me to problems.

I was thinking about this recently, and thought it might actually be easier to implement this somehow via something closer to the dataclass `__post_init__` than to how validators currently work.
I'm going to work on this soon, just haven't got a chance yet.
diff --git a/tests/test_generics.py b/tests/test_generics.py
--- a/tests/test_generics.py
+++ b/tests/test_generics.py
@@ -4,7 +4,7 @@
 
 import pytest
 
-from pydantic import BaseModel, ValidationError, validator
+from pydantic import BaseModel, ValidationError, root_validator, validator
 from pydantic.generics import GenericModel, _generic_types_cache
 
 skip_36 = pytest.mark.skipif(sys.version_info < (3, 7), reason='generics only supported for python 3.7 and above')
@@ -42,11 +42,17 @@ class Response(GenericModel, Generic[T]):
 
         @validator('data', each_item=True)
         def validate_value_nonzero(cls, v):
-            if isinstance(v, dict):
-                return v  # ensure v is actually a value of the dict, not the dict itself
             if v == 0:
                 raise ValueError('value is zero')
+            return v
+
+        @root_validator()
+        def validate_sum(cls, values):
+            if sum(values.get('data', {}).values()) > 5:
+                raise ValueError('sum too large')
+            return values
 
+    assert Response[Dict[int, int]](data={1: '4'}).dict() == {'data': {1: 4}}
     with pytest.raises(ValidationError) as exc_info:
         Response[Dict[int, int]](data={1: 'a'})
     assert exc_info.value.errors() == [
@@ -57,6 +63,10 @@ def validate_value_nonzero(cls, v):
         Response[Dict[int, int]](data={1: 0})
     assert exc_info.value.errors() == [{'loc': ('data', 1), 'msg': 'value is zero', 'type': 'value_error'}]
 
+    with pytest.raises(ValidationError) as exc_info:
+        Response[Dict[int, int]](data={1: 3, 2: 6})
+    assert exc_info.value.errors() == [{'loc': ('__root__',), 'msg': 'sum too large', 'type': 'value_error'}]
+
 
 @skip_36
 def test_methods_are_inherited():
diff --git a/tests/test_orm_mode.py b/tests/test_orm_mode.py
--- a/tests/test_orm_mode.py
+++ b/tests/test_orm_mode.py
@@ -1,8 +1,8 @@
-from typing import List
+from typing import Any, List
 
 import pytest
 
-from pydantic import BaseModel, ConfigError, ValidationError
+from pydantic import BaseModel, ConfigError, ValidationError, root_validator
 from pydantic.utils import GetterDict
 
 
@@ -26,7 +26,7 @@ def __getattr__(self, key):
 
     t = TestCls()
     gd = GetterDict(t)
-    assert gd.keys() == set()
+    assert gd.keys() == ['a', 'c', 'd']
     assert gd.get('a', None) == 1
     assert gd.get('b', None) is None
     assert gd.get('b', 1234) == 1234
@@ -34,6 +34,13 @@ def __getattr__(self, key):
     assert gd.get('d', None) == 4
     assert gd.get('e', None) == 5
     assert gd.get('f', 'missing') == 'missing'
+    assert list(gd.values()) == [1, 3, 4]
+    assert list(gd.items()) == [('a', 1), ('c', 3), ('d', 4)]
+    assert list(gd) == ['a', 'c', 'd']
+    assert gd == {'a': 1, 'c': 3, 'd': 4}
+    assert 'a' in gd
+    assert len(gd) == 3
+    assert str(gd) == "<GetterDict(TestCls) {'a': 1, 'c': 3, 'd': 4}>"
 
 
 def test_orm_mode():
@@ -166,3 +173,87 @@ class Config:
 
     model = Model.from_orm(TestCls())
     assert model.dict() == {'x': 1}
+
+
+def test_root_validator():
+    validator_value = None
+
+    class TestCls:
+        x = 1
+        y = 2
+
+    class Model(BaseModel):
+        x: int
+        y: int
+        z: int
+
+        @root_validator(pre=True)
+        def change_input_data(cls, value):
+            nonlocal validator_value
+            validator_value = value
+            return {**value, 'z': value['x'] + value['y']}
+
+        class Config:
+            orm_mode = True
+
+    model = Model.from_orm(TestCls())
+    assert model.dict() == {'x': 1, 'y': 2, 'z': 3}
+    assert isinstance(validator_value, GetterDict)
+    assert validator_value == {'x': 1, 'y': 2}
+
+
+def test_custom_getter_dict():
+    class TestCls:
+        x = 1
+        y = 2
+
+    def custom_getter_dict(obj):
+        assert isinstance(obj, TestCls)
+        return {'x': 42, 'y': 24}
+
+    class Model(BaseModel):
+        x: int
+        y: int
+
+        class Config:
+            orm_mode = True
+            getter_dict = custom_getter_dict
+
+    model = Model.from_orm(TestCls())
+    assert model.dict() == {'x': 42, 'y': 24}
+
+
+def test_custom_getter_dict_derived_model_class():
+    class CustomCollection:
+        __custom__ = True
+
+        def __iter__(self):
+            for elem in range(5):
+                yield elem
+
+    class Example:
+        def __init__(self, *args, **kwargs):
+            self.col = CustomCollection()
+            self.id = 1
+            self.name = 'name'
+
+    class MyGetterDict(GetterDict):
+        def get(self, key: Any, default: Any = None) -> Any:
+            res = getattr(self._obj, key, default)
+            if hasattr(res, '__custom__'):
+                return list(res)
+            return res
+
+    class ExampleBase(BaseModel):
+        name: str
+        col: List[int]
+
+    class ExampleOrm(ExampleBase):
+        id: int
+
+        class Config:
+            orm_mode = True
+            getter_dict = MyGetterDict
+
+    model = ExampleOrm.from_orm(Example())
+    assert model.dict() == {'name': 'name', 'col': [0, 1, 2, 3, 4], 'id': 1}
diff --git a/tests/test_parse.py b/tests/test_parse.py
--- a/tests/test_parse.py
+++ b/tests/test_parse.py
@@ -20,7 +20,7 @@ def test_parse_obj_fails():
     with pytest.raises(ValidationError) as exc_info:
         Model.parse_obj([1, 2, 3])
     assert exc_info.value.errors() == [
-        {'loc': ('__obj__',), 'msg': 'Model expected dict not list', 'type': 'type_error'}
+        {'loc': ('__root__',), 'msg': 'Model expected dict not list', 'type': 'type_error'}
     ]
 
 
@@ -84,14 +84,14 @@ def test_bad_ct():
     with pytest.raises(ValidationError) as exc_info:
         Model.parse_raw('{"a": 12, "b": 8}', content_type='application/missing')
     assert exc_info.value.errors() == [
-        {'loc': ('__obj__',), 'msg': 'Unknown content-type: application/missing', 'type': 'type_error'}
+        {'loc': ('__root__',), 'msg': 'Unknown content-type: application/missing', 'type': 'type_error'}
     ]
 
 
 def test_bad_proto():
     with pytest.raises(ValidationError) as exc_info:
         Model.parse_raw('{"a": 12, "b": 8}', proto='foobar')
-    assert exc_info.value.errors() == [{'loc': ('__obj__',), 'msg': 'Unknown protocol: foobar', 'type': 'type_error'}]
+    assert exc_info.value.errors() == [{'loc': ('__root__',), 'msg': 'Unknown protocol: foobar', 'type': 'type_error'}]
 
 
 def test_file_json(tmpdir):
diff --git a/tests/test_validators.py b/tests/test_validators.py
--- a/tests/test_validators.py
+++ b/tests/test_validators.py
@@ -3,8 +3,8 @@
 
 import pytest
 
-from pydantic import BaseModel, ConfigError, ValidationError, errors, validator
-from pydantic.class_validators import make_generic_validator
+from pydantic import BaseModel, ConfigError, Extra, ValidationError, errors, validator
+from pydantic.class_validators import make_generic_validator, root_validator
 
 
 def test_simple():
@@ -715,3 +715,167 @@ class Model(BaseModel):
             @validator('x', whole=True)
             def check_something(cls, v):
                 return v
+
+
+def test_root_validator():
+    root_val_values = []
+
+    class Model(BaseModel):
+        a: int = 1
+        b: str
+
+        @validator('b')
+        def repeat_b(cls, v):
+            return v * 2
+
+        @root_validator
+        def root_validator(cls, values):
+            root_val_values.append(values)
+            if 'snap' in values.get('b', ''):
+                raise ValueError('foobar')
+            return dict(values, b='changed')
+
+    assert Model(a='123', b='bar').dict() == {'a': 123, 'b': 'changed'}
+
+    with pytest.raises(ValidationError) as exc_info:
+        Model(b='snap dragon')
+    assert exc_info.value.errors() == [{'loc': ('__root__',), 'msg': 'foobar', 'type': 'value_error'}]
+
+    with pytest.raises(ValidationError) as exc_info:
+        Model(a='broken', b='bar')
+    assert exc_info.value.errors() == [
+        {'loc': ('a',), 'msg': 'value is not a valid integer', 'type': 'type_error.integer'}
+    ]
+
+    assert root_val_values == [{'a': 123, 'b': 'barbar'}, {'a': 1, 'b': 'snap dragonsnap dragon'}, {'b': 'barbar'}]
+
+
+def test_root_validator_pre():
+    root_val_values = []
+
+    class Model(BaseModel):
+        a: int = 1
+        b: str
+
+        @validator('b')
+        def repeat_b(cls, v):
+            return v * 2
+
+        @root_validator(pre=True)
+        def root_validator(cls, values):
+            root_val_values.append(values)
+            if 'snap' in values.get('b', ''):
+                raise ValueError('foobar')
+            return {'a': 42, 'b': 'changed'}
+
+    assert Model(a='123', b='bar').dict() == {'a': 42, 'b': 'changedchanged'}
+
+    with pytest.raises(ValidationError) as exc_info:
+        Model(b='snap dragon')
+
+    assert root_val_values == [{'a': '123', 'b': 'bar'}, {'b': 'snap dragon'}]
+    assert exc_info.value.errors() == [{'loc': ('__root__',), 'msg': 'foobar', 'type': 'value_error'}]
+
+
+def test_root_validator_repeat():
+    with pytest.raises(errors.ConfigError, match='duplicate validator function'):
+
+        class Model(BaseModel):
+            a: int = 1
+
+            @root_validator
+            def root_validator_repeated(cls, values):
+                return values
+
+            @root_validator  # noqa: F811
+            def root_validator_repeated(cls, values):
+                return values
+
+
+def test_root_validator_repeat2():
+    with pytest.raises(errors.ConfigError, match='duplicate validator function'):
+
+        class Model(BaseModel):
+            a: int = 1
+
+            @validator('a')
+            def repeat_validator(cls, v):
+                return v
+
+            @root_validator(pre=True)  # noqa: F811
+            def repeat_validator(cls, values):
+                return values
+
+
+def test_root_validator_self():
+    with pytest.raises(
+        errors.ConfigError, match=r'Invalid signature for root validator root_validator: \(self, values\)'
+    ):
+
+        class Model(BaseModel):
+            a: int = 1
+
+            @root_validator
+            def root_validator(self, values):
+                return values
+
+
+def test_root_validator_extra():
+    with pytest.raises(errors.ConfigError) as exc_info:
+
+        class Model(BaseModel):
+            a: int = 1
+
+            @root_validator
+            def root_validator(cls, values, another):
+                return values
+
+    assert str(exc_info.value) == (
+        'Invalid signature for root validator root_validator: (cls, values, another), should be: (cls, values).'
+    )
+
+
+def test_root_validator_types():
+    root_val_values = None
+
+    class Model(BaseModel):
+        a: int = 1
+        b: str
+
+        @root_validator
+        def root_validator(cls, values):
+            nonlocal root_val_values
+            root_val_values = cls, values
+            return values
+
+        class Config:
+            extra = Extra.allow
+
+    assert Model(b='bar', c='wobble').dict() == {'a': 1, 'b': 'bar', 'c': 'wobble'}
+
+    assert root_val_values == (Model, {'a': 1, 'b': 'bar', 'c': 'wobble'})
+
+
+def test_root_validator_inheritance():
+    calls = []
+
+    class Parent(BaseModel):
+        pass
+
+        @root_validator
+        def root_validator_parent(cls, values):
+            calls.append(f'parent validator: {values}')
+            return {'extra1': 1, **values}
+
+    class Child(Parent):
+        a: int
+
+        @root_validator
+        def root_validator_child(cls, values):
+            calls.append(f'child validator: {values}')
+            return {'extra2': 2, **values}
+
+    assert len(Child.__post_root_validators__) == 2
+    assert len(Child.__pre_root_validators__) == 0
+    assert Child(a=123).dict() == {'extra2': 2, 'extra1': 1, 'a': 123}
+    assert calls == ["parent validator: {'a': 123}", "child validator: {'extra1': 1, 'a': 123}"]
diff --git a/tests/test_validators_dataclass.py b/tests/test_validators_dataclass.py
--- a/tests/test_validators_dataclass.py
+++ b/tests/test_validators_dataclass.py
@@ -3,7 +3,7 @@
 
 import pytest
 
-from pydantic import ValidationError, validator
+from pydantic import ValidationError, root_validator, validator
 from pydantic.dataclasses import dataclass
 
 
@@ -108,3 +108,31 @@ def add_to_a(cls, v):
             return v + 5
 
     assert Child(a=0).a == 5
+
+
+def test_root_validator():
+    root_val_values = []
+
+    @dataclass
+    class MyDataclass:
+        a: int
+        b: str
+
+        @validator('b')
+        def repeat_b(cls, v):
+            return v * 2
+
+        @root_validator
+        def root_validator(cls, values):
+            root_val_values.append(values)
+            if 'snap' in values.get('b', ''):
+                raise ValueError('foobar')
+            return dict(values, b='changed')
+
+    assert asdict(MyDataclass(a='123', b='bar')) == {'a': 123, 'b': 'changed'}
+
+    with pytest.raises(ValidationError) as exc_info:
+        MyDataclass(a=1, b='snap dragon')
+    assert root_val_values == [{'a': 123, 'b': 'barbar'}, {'a': 1, 'b': 'snap dragonsnap dragon'}]
+
+    assert exc_info.value.errors() == [{'loc': ('__root__',), 'msg': 'foobar', 'type': 'value_error'}]

Root Errors and "__obj__" vs "__root__"
Currently [here](https://github.com/samuelcolvin/pydantic/blob/master/pydantic/main.py#L343) (for invalid data to `parse_obj`) and [here](https://github.com/samuelcolvin/pydantic/blob/master/pydantic/main.py#L361) (in `parse_raw`) we use `'__obj__'` as the location for errors to indicate an error which is general to the model, not specific to a field.

We should change this in v1 to `__root__` to better match other nomenclature, eg. custom root types, where we use `__root__`.

We should also implement at some point entire model validation, as discussed at https://github.com/samuelcolvin/pydantic/issues/691#issuecomment-518318096. I guess to match the above naming, we should do this using a special value to a validator `@validator('__root__')`. If this raised an error it would end up in `ValidationError` details with `'location': '__root__'`, (Unless it's a "`@validator('__root__')`" validator for a submodel, when obviously it should have the location of that model. 

Perhaps it would would be nice to have a special decorator `@root_validator` which is an alias of `@validator('__root__')`, we should support multiple root validators either as a result of inheritance or on a single class.

I guess the `__obj__` > `__root__` change must happen with v1 and the new root validator could go in a later release, but we should be sure we won't need other backwards incompatible changes to implement the root validator.

Thoughts?

tests/test_generics.py::test_generic_name tests/test_generics.py::test_double_parameterize_error tests/test_generics.py::test_value_validation tests/test_generics.py::test_methods_are_inherited tests/test_generics.py::test_config_is_inherited tests/test_generics.py::test_default_argument tests/test_generics.py::test_default_argument_for_typevar tests/test_generics.py::test_classvar tests/test_generics.py::test_non_annotated_field tests/test_generics.py::test_must_inherit_from_generic tests/test_generics.py::test_parameters_must_be_typevar tests/test_generics.py::test_subclass_can_be_genericized tests/test_generics.py::test_parameter_count tests/test_generics.py::test_cover_cache tests/test_generics.py::test_generic_config tests/test_generics.py::test_generic_instantiation_error tests/test_generics.py::test_parameterized_generic_instantiation_error tests/test_generics.py::test_deep_generic tests/test_generics.py::test_enum_generic tests/test_generics.py::test_generic 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tests/test_validators.py::test_make_generic_validator[fields12-_cls_,_v_,_config_] tests/test_validators.py::test_make_generic_validator[fields13-_cls_,_v_,_values_] tests/test_validators.py::test_make_generic_validator[fields14-_cls_,_v_,_field_,_config_] tests/test_validators.py::test_make_generic_validator[fields15-_cls_,_v_,_field_,_values_] tests/test_validators.py::test_make_generic_validator[fields16-_cls_,_v_,_config_,_values_] tests/test_validators.py::test_make_generic_validator[fields17-_cls_,_v_,_field_,_values_,_config_] tests/test_validators.py::test_make_generic_validator_kwargs tests/test_validators.py::test_make_generic_validator_invalid tests/test_validators.py::test_make_generic_validator_cls_kwargs tests/test_validators.py::test_make_generic_validator_cls_invalid tests/test_validators.py::test_make_generic_validator_self tests/test_validators.py::test_assert_raises_validation_error tests/test_validators.py::test_optional_validator tests/test_validators.py::test_whole tests/test_validators.py::test_root_validator tests/test_validators.py::test_root_validator_pre tests/test_validators.py::test_root_validator_repeat tests/test_validators.py::test_root_validator_repeat2 tests/test_validators.py::test_root_validator_self tests/test_validators.py::test_root_validator_extra tests/test_validators.py::test_root_validator_types tests/test_validators.py::test_root_validator_inheritance tests/test_validators_dataclass.py::test_simple tests/test_validators_dataclass.py::test_validate_pre tests/test_validators_dataclass.py::test_validate_multiple tests/test_validators_dataclass.py::test_classmethod tests/test_validators_dataclass.py::test_validate_parent tests/test_validators_dataclass.py::test_inheritance_replace tests/test_validators_dataclass.py::test_root_validator