diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index aa7b3ff..8e181b1 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -17,6 +17,8 @@ Added
   `#468 <https://github.com/joke2k/django-environ/pull/468>`_.
 - Added capability to handle comments after #, after quoted values, like ``KEY= 'part1 # part2' # comment``
   `#475 <https://github.com/joke2k/django-environ/pull/475>`_.
+- Added support for ``interpolate`` parameter
+  `#419 <https://github.com/joke2k/django-environ/pull/419>`_.
 
 Changed
 +++++++
diff --git a/docs/tips.rst b/docs/tips.rst
index 20b8c3e..ab59f69 100644
--- a/docs/tips.rst
+++ b/docs/tips.rst
@@ -226,7 +226,7 @@ Proxy value
 ===========
 
 Values that being with a ``$`` may be interpolated. Pass ``interpolate=True`` to
-``environ.Env()`` to enable this feature:
+``environ.Env()`` to enable this feature (``True`` by default):
 
 .. code-block:: python
 
diff --git a/environ/environ.py b/environ/environ.py
index 644286e..f35470c 100644
--- a/environ/environ.py
+++ b/environ/environ.py
@@ -197,11 +197,12 @@ class Env:
     VAR = re.compile(r'(?<!\\)\$\{?(?P<name>[A-Z_][0-9A-Z_]*)}?',
                      re.IGNORECASE)
 
-    def __init__(self, **scheme):
+    def __init__(self, interpolate=True, **scheme):
         self._local = threading.local()
         self.smart_cast = True
         self.escape_proxy = False
         self.prefix = ""
+        self.interpolate = interpolate
         self.scheme = scheme
 
     def __call__(self, var, cast=None, default=NOTSET, parse_default=False):
@@ -425,7 +426,8 @@ class Env:
             value = default
 
         # Expand variables
-        if isinstance(value, (bytes, str)) and var_name not in NOT_EXPANDED:
+        if self.interpolate and isinstance(value, (bytes, str)) \
+                and var_name not in NOT_EXPANDED:
             def repl(match_):
                 return self.get_value(
                     match_.group('name'), cast=cast, default=default,

diff --git a/tests/test_env.py b/tests/test_env.py
index 0b105f5..1f2df15 100644
--- a/tests/test_env.py
+++ b/tests/test_env.py
@@ -134,6 +134,10 @@ class TestEnv:
     def test_proxied_value(self):
         assert self.env('PROXIED_VAR') == 'bar'
 
+    def test_not_interpolated_proxied_value(self):
+        env = Env(interpolate=False)
+        assert env('PROXIED_VAR') == '$STR_VAR'
+
     def test_escaped_dollar_sign(self):
         self.env.escape_proxy = True
         assert self.env('ESCAPED_VAR') == '$baz'

`interpolate` flag functionality is not implemented
I did `SECRET_KEY = env('DJANGO_SECRET_KEY')` and got the error:

```
django.core.exceptions.ImproperlyConfigured: Set the a&d3*0k#skh)!5o)$))zz9&%hr@-akid5zh--05ei790+wn0$r environment variable
```

This is becuase my `DJANGO_SECRET_KEY` starts with the dollar sign: 

```
DJANGO_SECRET_KEY="$a&d3*0k#skh)!5o)$))zz9&%hr@-akid5zh--05ei790+wn0$r"
```

There was a number of issues for this problem: #284, #60, #271.

Eventually, #333 somewhat solved the issue by allowing to escape the dollar sign. But this is not the best approach for generated values such as secret keys. The better option would be an ability to disable interpolation altogether. Ideally by default since the behaviour is unexpected.

Interestingly, the `interpolation` flag is described in the docs: https://django-environ.readthedocs.io/en/latest/tips.html?highlight=Proxied%20Values#proxy-value. BUT it's not implemented! [This commit ](https://github.com/joke2k/django-environ/commit/f8c8a1ff50109e1b6de99e3f6ad51b326a794392) introduced the doc. Apparently, the implementation (#145) was not merged and closed in favor of #333. I don't know why. #145 seems like a proper solution.
tests/test_env.py::TestEnv::test_not_interpolated_proxied_value tests/test_env.py::TestFileEnv::test_not_interpolated_proxied_value tests/test_env.py::TestSubClass::test_not_interpolated_proxied_value
tests/test_env.py::TestEnv::test_not_present_with_default tests/test_env.py::TestEnv::test_not_present_without_default tests/test_env.py::TestEnv::test_contains tests/test_env.py::TestEnv::test_str[STR_VAR-bar-False] tests/test_env.py::TestEnv::test_str[MULTILINE_STR_VAR-foo\\nbar-False] tests/test_env.py::TestEnv::test_str[MULTILINE_STR_VAR-foo\nbar-True] tests/test_env.py::TestEnv::test_str[MULTILINE_QUOTED_STR_VAR----BEGIN---\\r\\n---END----False] tests/test_env.py::TestEnv::test_str[MULTILINE_QUOTED_STR_VAR----BEGIN---\n---END----True] tests/test_env.py::TestEnv::test_str[MULTILINE_ESCAPED_STR_VAR----BEGIN---\\\\n---END----False] tests/test_env.py::TestEnv::test_str[MULTILINE_ESCAPED_STR_VAR----BEGIN---\\\n---END----True] tests/test_env.py::TestEnv::test_bytes[STR_VAR-bar-default0] tests/test_env.py::TestEnv::test_bytes[NON_EXISTENT_BYTES_VAR-some-default-some-default] tests/test_env.py::TestEnv::test_bytes[NON_EXISTENT_STR_VAR-some-default-some-default] tests/test_env.py::TestEnv::test_int tests/test_env.py::TestEnv::test_int_with_none_default tests/test_env.py::TestEnv::test_float[33.3-FLOAT_VAR] tests/test_env.py::TestEnv::test_float[33.3-FLOAT_COMMA_VAR] tests/test_env.py::TestEnv::test_float[123420333.3-FLOAT_STRANGE_VAR1] tests/test_env.py::TestEnv::test_float[123420333.3-FLOAT_STRANGE_VAR2] tests/test_env.py::TestEnv::test_float[-1.0-FLOAT_NEGATIVE_VAR] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_LIKE_INT] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_LIKE_BOOL] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_LIKE_BOOL_WITH_COMMENT] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_INT] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_BOOL] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_BOOL_WITH_COMMENT] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_1] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_2] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_3] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_4] tests/test_env.py::TestEnv::test_bool_true[True-BOOL_TRUE_STRING_5] tests/test_env.py::TestEnv::test_bool_true[False-BOOL_FALSE_STRING_LIKE_INT] tests/test_env.py::TestEnv::test_bool_true[False-BOOL_FALSE_INT] tests/test_env.py::TestEnv::test_bool_true[False-BOOL_FALSE_STRING_LIKE_BOOL] tests/test_env.py::TestEnv::test_bool_true[False-BOOL_FALSE_BOOL] tests/test_env.py::TestEnv::test_proxied_value tests/test_env.py::TestEnv::test_escaped_dollar_sign tests/test_env.py::TestEnv::test_escaped_dollar_sign_disabled tests/test_env.py::TestEnv::test_int_list tests/test_env.py::TestEnv::test_int_list_cast_tuple tests/test_env.py::TestEnv::test_int_tuple tests/test_env.py::TestEnv::test_mix_tuple_issue_387 tests/test_env.py::TestEnv::test_str_list_with_spaces tests/test_env.py::TestEnv::test_empty_list tests/test_env.py::TestEnv::test_dict_value tests/test_env.py::TestEnv::test_complex_dict_value tests/test_env.py::TestEnv::test_dict_parsing[dict] tests/test_env.py::TestEnv::test_dict_parsing[dict_int] tests/test_env.py::TestEnv::test_dict_parsing[dict_float] tests/test_env.py::TestEnv::test_dict_parsing[dict_str_list] tests/test_env.py::TestEnv::test_dict_parsing[dict_int_list] tests/test_env.py::TestEnv::test_dict_parsing[dict_int_cast] tests/test_env.py::TestEnv::test_dict_parsing[dict_str_cast] tests/test_env.py::TestEnv::test_url_value tests/test_env.py::TestEnv::test_url_empty_string_default_value tests/test_env.py::TestEnv::test_url_encoded_parts tests/test_env.py::TestEnv::test_db_url_value[postgres] tests/test_env.py::TestEnv::test_db_url_value[mysql] tests/test_env.py::TestEnv::test_db_url_value[mysql_gis] tests/test_env.py::TestEnv::test_db_url_value[oracle_tns] tests/test_env.py::TestEnv::test_db_url_value[oracle] tests/test_env.py::TestEnv::test_db_url_value[redshift] tests/test_env.py::TestEnv::test_db_url_value[sqlite] tests/test_env.py::TestEnv::test_db_url_value[custom] tests/test_env.py::TestEnv::test_db_url_value[cloudsql] tests/test_env.py::TestEnv::test_cache_url_value[memcached] tests/test_env.py::TestEnv::test_cache_url_value[redis] tests/test_env.py::TestEnv::test_email_url_value tests/test_env.py::TestEnv::test_json_value tests/test_env.py::TestEnv::test_path tests/test_env.py::TestEnv::test_smart_cast tests/test_env.py::TestEnv::test_exported tests/test_env.py::TestEnv::test_prefix tests/test_env.py::TestFileEnv::test_not_present_with_default tests/test_env.py::TestFileEnv::test_not_present_without_default tests/test_env.py::TestFileEnv::test_contains tests/test_env.py::TestFileEnv::test_str[STR_VAR-bar-False] tests/test_env.py::TestFileEnv::test_str[MULTILINE_STR_VAR-foo\\nbar-False] tests/test_env.py::TestFileEnv::test_str[MULTILINE_STR_VAR-foo\nbar-True] tests/test_env.py::TestFileEnv::test_str[MULTILINE_QUOTED_STR_VAR----BEGIN---\\r\\n---END----False] tests/test_env.py::TestFileEnv::test_str[MULTILINE_QUOTED_STR_VAR----BEGIN---\n---END----True] tests/test_env.py::TestFileEnv::test_str[MULTILINE_ESCAPED_STR_VAR----BEGIN---\\\\n---END----False] tests/test_env.py::TestFileEnv::test_str[MULTILINE_ESCAPED_STR_VAR----BEGIN---\\\n---END----True] tests/test_env.py::TestFileEnv::test_bytes[STR_VAR-bar-default0] tests/test_env.py::TestFileEnv::test_bytes[NON_EXISTENT_BYTES_VAR-some-default-some-default] tests/test_env.py::TestFileEnv::test_bytes[NON_EXISTENT_STR_VAR-some-default-some-default] tests/test_env.py::TestFileEnv::test_int tests/test_env.py::TestFileEnv::test_int_with_none_default tests/test_env.py::TestFileEnv::test_float[33.3-FLOAT_VAR] tests/test_env.py::TestFileEnv::test_float[33.3-FLOAT_COMMA_VAR] tests/test_env.py::TestFileEnv::test_float[123420333.3-FLOAT_STRANGE_VAR1] tests/test_env.py::TestFileEnv::test_float[123420333.3-FLOAT_STRANGE_VAR2] tests/test_env.py::TestFileEnv::test_float[-1.0-FLOAT_NEGATIVE_VAR] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_LIKE_INT] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_LIKE_BOOL] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_LIKE_BOOL_WITH_COMMENT] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_INT] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_BOOL] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_BOOL_WITH_COMMENT] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_1] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_2] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_3] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_4] tests/test_env.py::TestFileEnv::test_bool_true[True-BOOL_TRUE_STRING_5] tests/test_env.py::TestFileEnv::test_bool_true[False-BOOL_FALSE_STRING_LIKE_INT] tests/test_env.py::TestFileEnv::test_bool_true[False-BOOL_FALSE_INT] tests/test_env.py::TestFileEnv::test_bool_true[False-BOOL_FALSE_STRING_LIKE_BOOL] tests/test_env.py::TestFileEnv::test_bool_true[False-BOOL_FALSE_BOOL] tests/test_env.py::TestFileEnv::test_proxied_value tests/test_env.py::TestFileEnv::test_escaped_dollar_sign tests/test_env.py::TestFileEnv::test_escaped_dollar_sign_disabled tests/test_env.py::TestFileEnv::test_int_list tests/test_env.py::TestFileEnv::test_int_list_cast_tuple tests/test_env.py::TestFileEnv::test_int_tuple tests/test_env.py::TestFileEnv::test_mix_tuple_issue_387 tests/test_env.py::TestFileEnv::test_str_list_with_spaces tests/test_env.py::TestFileEnv::test_empty_list tests/test_env.py::TestFileEnv::test_dict_value tests/test_env.py::TestFileEnv::test_complex_dict_value tests/test_env.py::TestFileEnv::test_dict_parsing[dict] tests/test_env.py::TestFileEnv::test_dict_parsing[dict_int] tests/test_env.py::TestFileEnv::test_dict_parsing[dict_float] tests/test_env.py::TestFileEnv::test_dict_parsing[dict_str_list] tests/test_env.py::TestFileEnv::test_dict_parsing[dict_int_list] tests/test_env.py::TestFileEnv::test_dict_parsing[dict_int_cast] tests/test_env.py::TestFileEnv::test_dict_parsing[dict_str_cast] tests/test_env.py::TestFileEnv::test_url_value tests/test_env.py::TestFileEnv::test_url_empty_string_default_value tests/test_env.py::TestFileEnv::test_url_encoded_parts tests/test_env.py::TestFileEnv::test_db_url_value[postgres] tests/test_env.py::TestFileEnv::test_db_url_value[mysql] tests/test_env.py::TestFileEnv::test_db_url_value[mysql_gis] tests/test_env.py::TestFileEnv::test_db_url_value[oracle_tns] tests/test_env.py::TestFileEnv::test_db_url_value[oracle] tests/test_env.py::TestFileEnv::test_db_url_value[redshift] tests/test_env.py::TestFileEnv::test_db_url_value[sqlite] tests/test_env.py::TestFileEnv::test_db_url_value[custom] tests/test_env.py::TestFileEnv::test_db_url_value[cloudsql] tests/test_env.py::TestFileEnv::test_cache_url_value[memcached] tests/test_env.py::TestFileEnv::test_cache_url_value[redis] tests/test_env.py::TestFileEnv::test_email_url_value tests/test_env.py::TestFileEnv::test_json_value tests/test_env.py::TestFileEnv::test_path tests/test_env.py::TestFileEnv::test_smart_cast tests/test_env.py::TestFileEnv::test_exported tests/test_env.py::TestFileEnv::test_prefix tests/test_env.py::TestFileEnv::test_read_env_path_like tests/test_env.py::TestFileEnv::test_existing_overwrite[True] tests/test_env.py::TestFileEnv::test_existing_overwrite[False] tests/test_env.py::TestSubClass::test_not_present_with_default tests/test_env.py::TestSubClass::test_not_present_without_default tests/test_env.py::TestSubClass::test_contains tests/test_env.py::TestSubClass::test_str[STR_VAR-bar-False] tests/test_env.py::TestSubClass::test_str[MULTILINE_STR_VAR-foo\\nbar-False] tests/test_env.py::TestSubClass::test_str[MULTILINE_STR_VAR-foo\nbar-True] tests/test_env.py::TestSubClass::test_str[MULTILINE_QUOTED_STR_VAR----BEGIN---\\r\\n---END----False] tests/test_env.py::TestSubClass::test_str[MULTILINE_QUOTED_STR_VAR----BEGIN---\n---END----True] tests/test_env.py::TestSubClass::test_str[MULTILINE_ESCAPED_STR_VAR----BEGIN---\\\\n---END----False] tests/test_env.py::TestSubClass::test_str[MULTILINE_ESCAPED_STR_VAR----BEGIN---\\\n---END----True] tests/test_env.py::TestSubClass::test_bytes[STR_VAR-bar-default0] tests/test_env.py::TestSubClass::test_bytes[NON_EXISTENT_BYTES_VAR-some-default-some-default] tests/test_env.py::TestSubClass::test_bytes[NON_EXISTENT_STR_VAR-some-default-some-default] tests/test_env.py::TestSubClass::test_int tests/test_env.py::TestSubClass::test_int_with_none_default tests/test_env.py::TestSubClass::test_float[33.3-FLOAT_VAR] tests/test_env.py::TestSubClass::test_float[33.3-FLOAT_COMMA_VAR] tests/test_env.py::TestSubClass::test_float[123420333.3-FLOAT_STRANGE_VAR1] tests/test_env.py::TestSubClass::test_float[123420333.3-FLOAT_STRANGE_VAR2] tests/test_env.py::TestSubClass::test_float[-1.0-FLOAT_NEGATIVE_VAR] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_LIKE_INT] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_LIKE_BOOL] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_LIKE_BOOL_WITH_COMMENT] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_INT] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_BOOL] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_BOOL_WITH_COMMENT] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_1] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_2] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_3] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_4] tests/test_env.py::TestSubClass::test_bool_true[True-BOOL_TRUE_STRING_5] tests/test_env.py::TestSubClass::test_bool_true[False-BOOL_FALSE_STRING_LIKE_INT] tests/test_env.py::TestSubClass::test_bool_true[False-BOOL_FALSE_INT] tests/test_env.py::TestSubClass::test_bool_true[False-BOOL_FALSE_STRING_LIKE_BOOL] tests/test_env.py::TestSubClass::test_bool_true[False-BOOL_FALSE_BOOL] tests/test_env.py::TestSubClass::test_proxied_value tests/test_env.py::TestSubClass::test_escaped_dollar_sign tests/test_env.py::TestSubClass::test_escaped_dollar_sign_disabled tests/test_env.py::TestSubClass::test_int_list tests/test_env.py::TestSubClass::test_int_list_cast_tuple tests/test_env.py::TestSubClass::test_int_tuple tests/test_env.py::TestSubClass::test_mix_tuple_issue_387 tests/test_env.py::TestSubClass::test_str_list_with_spaces tests/test_env.py::TestSubClass::test_empty_list tests/test_env.py::TestSubClass::test_dict_value tests/test_env.py::TestSubClass::test_complex_dict_value tests/test_env.py::TestSubClass::test_dict_parsing[dict] tests/test_env.py::TestSubClass::test_dict_parsing[dict_int] tests/test_env.py::TestSubClass::test_dict_parsing[dict_float] tests/test_env.py::TestSubClass::test_dict_parsing[dict_str_list] tests/test_env.py::TestSubClass::test_dict_parsing[dict_int_list] tests/test_env.py::TestSubClass::test_dict_parsing[dict_int_cast] tests/test_env.py::TestSubClass::test_dict_parsing[dict_str_cast] tests/test_env.py::TestSubClass::test_url_value tests/test_env.py::TestSubClass::test_url_empty_string_default_value tests/test_env.py::TestSubClass::test_url_encoded_parts tests/test_env.py::TestSubClass::test_db_url_value[postgres] tests/test_env.py::TestSubClass::test_db_url_value[mysql] tests/test_env.py::TestSubClass::test_db_url_value[mysql_gis] tests/test_env.py::TestSubClass::test_db_url_value[oracle_tns] tests/test_env.py::TestSubClass::test_db_url_value[oracle] tests/test_env.py::TestSubClass::test_db_url_value[redshift] tests/test_env.py::TestSubClass::test_db_url_value[sqlite] tests/test_env.py::TestSubClass::test_db_url_value[custom] tests/test_env.py::TestSubClass::test_db_url_value[cloudsql] tests/test_env.py::TestSubClass::test_cache_url_value[memcached] tests/test_env.py::TestSubClass::test_cache_url_value[redis] tests/test_env.py::TestSubClass::test_email_url_value tests/test_env.py::TestSubClass::test_json_value tests/test_env.py::TestSubClass::test_path tests/test_env.py::TestSubClass::test_smart_cast tests/test_env.py::TestSubClass::test_exported tests/test_env.py::TestSubClass::test_prefix tests/test_env.py::TestSubClass::test_singleton_environ