Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. CIL (C Intermediate Language) is a simplified subset of the C programming language, as well as a set of tools for transforming C programs into that language. Several other tools use CIL as a way to have access to a C abstract syntax tree. Some of this programs are Frama-c (Framework to analyze C programs) or Compcert (C compiler proven in coq). CIL was originally designed and implemented by George Necula et al. in 2002.