From BlenderWiki  Jump to: navigation, search   Render Baking
Mode: All Modes except Sculpt  Panel: Scene (F10) Render Context
→ Bake panel  Hotkey: CtrlAltB  Menu: Render → Bake Render
Meshes   The Bake tab in the Render buttons panel.     Can
significantly reduce render times Texture painting made easier
Reduced polygon count Repeated renders are made faster,
multiplying the time savings Object must be UV-unwrapped.  You
apply the baked Normal image as a Normal Map using a Texture
channel.   Full Render Ambient Occlusion Bakes ambient occlusion
as specified in the World panels (F8). Ignores all lights in the
scene. Bakes colors of materials and textures only, without
shading. Mesh Must be Visible in Render If a mesh not is visible
in regular render, for example because it is disabled for
rendering in the Outliner or has the DupliVerts setting enabled,
it cannot be baked to.  Options under development (after 2.45)
The Bake tab in the Render buttons panel.Development version
Read more here: Changes since 2