If you are using a released version of LLVM, see the download page to find your documentation.
The LLVM compiler infrastructure supports a wide range of projects, from industrial strength compilers to specialized JIT applications to small research projects.
Similarly, documentation is broken down into several high-level groupings targeted at different audiences:
Several introductory papers and presentations are available at LLVM Design & Overview.
The list of publications based on LLVM.
Those new to the LLVM system should first visit the User Guides.
NOTE: If you are a user who is only interested in using LLVM-based compilers, you should look into Clang or DragonEgg instead. The documentation here is intended for users who have a need to work with the intermediate LLVM representation.
Developers of applications which use LLVM as a library should visit the Programming Documentation.
API clients and LLVM developers may be interested in the Subsystem Documentation documentation.
Additional documentation on the LLVM project can be found at Development Process Documentation.
For more information, consider consulting the LLVM Mailing Lists.