The LLVM Project is a collection of modular and reusable compiler and toolchain technologies. Despite its name, LLVM has little to do with traditional virtual machines. LLVM began as a research project at the University of Illinois, with the goal of providing a modern, SSA-based compilation strategy capable of supporting both static and dynamic compilation of arbitrary programming languages. Since then, LLVM has grown to be an umbrella project consisting of a number of different subprojects, many of which are being used in production by a wide variety of commercial and open source projects as well as being widely used in academic research.

The primary sub-projects of LLVM are:

• The LLVM Core libraries provide a modern source- and target-independent optimizer, along with code generation support for many popular CPUs. These libraries are built around a well specified code representation known as the LLVM intermediate representation ("LLVM IR").
• Clang is an "LLVM native" C/C++/Objective-C compiler, which aims to deliver amazingly fast compiles, extremely useful error and warning messages and to provide a platform for building great source level tools. The Clang Static Analyzer is a clang-based tool that automatically finds bugs in your code.
• The LLDB project builds on libraries provided by LLVM and Clang to provide a great native debugger on top of Clang and LLVM libraries.
• The libc++ and libc++ ABI projects provide a standard conformant and high-performance implementation of the C++ Standard Library.
• The MLIR subproject aims to address software fragmentation, compilation for heterogeneous hardware, significantly reduce the cost of building domain specific compilers, and aid in connecting existing compilers.
• The lld project aims to be the built-in linker for clang/llvm. Currently, clang must invoke the system linker to produce executables.
• In addition to official subprojects of LLVM, there are a broad variety of projects that use components of LLVM for various tasks.