The 16th annual International Conference on the Principles and Practice of Constraint Programming (CP 2010) was held in St. Andrews, Scotland, during September 6–10, 2010. We would like to thank our sponsors for their generous support of this event. This conference is concerned with all aspects of computing with constraints, including:theory,algorithms,applications,environments,languages,modelsand systems. We received a wide variety of submissions, each of which was reviewed by at least three referees. Referees were chosen for each submission by an initial bidding process where Program Committee members chose papers from their area of interest. The range of expertise represented by the large Program C- mittee meant that almost all submissions were reviewed by subject experts on the Program Committee, or by colleagues chosen by members of the Program Committee for their particular expertise. Papers weresolicitedeither as long (15 page), or short (8 page) submissions. Short-paper submissions were refereed to exactly the same high standards as long-paper submissions but naturally were expected to contain a smaller quantity of new material. Thus there is no disti- tion in these proceedings between short and long papers. I used the excellent EasyChair conference management system to support this process of reviewing, and for the collation and organization of these proceedings. Submissions were made either to the applications track or to the research track. Therewere101(23short)researchtracksubmissionsofwhich36(8short) wereaccepted,whichisa36%(35%ofshort)acceptancerate. Applicationstrack submissions received special consideration and the acceptance rate was sign- cantly higher than for the research track.