This book constitutes the refereed proceedings of the 11th International Conference on Principles and Practice of Constraint Programming, CP 2005, held in Sitges, Spain, in October 2005.

The 48 revised full papers and 22 revised short papers presented together with extended abstracts of 4 invited talks and 40 abstracts of contributions to the doctoral students program as well as 7 abstracts of contributions to a systems demonstration session were carefully reviewed and selected from 164 submissions. All current issues of computing with constraints are addressed, ranging from methodological and foundational aspects to solving real-world problems in various application fields.