This book constitutes the refereed proceedings of the 21st International Workshop on Computer Science Logic, CSL 2007, held as the 16th Annual Conference of the EACSL in Lausanne, Switzerland, in September 2007.

The 36 revised full papers presented together with the abstracts of 6 invited lectures were carefully reviewed and selected from 116 submissions. The papers are organized in topical sections on logic and games, expressiveness, games and trees, logic and deduction, lambda calculus, finite model theory, linear logic, proof theory, and game semantics.