This book constitutes the thoroughly refereed post-proceedings of the 6th International Workshop on Privacy Enhancing Technologies, PET 2006, held in Cambridge, UK, in June 2006 co-located with WEIS 2006, the Workshop on the Economics of Information Security, and WOTE 2006, the IAVoSS Workshop On Trustworthy Elections. The 24 revised full papers present novel research on all theoretical and practical aspects of privacy technologies.