This book constitutes the proceedings of the Third International Conference on Information Theoretic Security, held in Calgary, Canada, in August 2008. The 14 papers presented in this volume were carefully reviewed and selected from 43 submissions. There were nine invited speeches to the conference. The topics covered are secure and reliable communication; quantum information and communication; networks and devices; multiparty computation; information hiding and tracing; coding theory and security; quantum computation; foundation; and encryption.