This book constitutes the thoroughly refereed post-proceedings of the Third International Workshop on Learning Classifier Systems, IWLCS 2000, held in Paris, France in September 2000. The 13 revised full papers presented have gone through two rounds of reviewing and selection. Also included is a comprehensive LCS bibliography listing more than 600 entries as well as an appendix. The papers are organized in topical sections on theory, applications, and advanced architectures.