As computer science enters the new millennium, methods and languages for reasoning with constraints have come to play an important role, with both t- oretical advances and practical applications. Constraints have emerged as the basis of a representational and computational paradigm that draws from many disciplinesandcanbebroughttobearonmanyproblemdomains,includingar- ?cial intelligence, databases, and combinatorial optimization. The conference is concerned with all aspects of computing with constraints including algorithms, applications, environments, languages, models and systems. The Sixth InternationalConference on Principles and Practiceof Constraint Programming (CP2000) continues to provide an international forum for p- senting and discussing state-of-the-art research and applications involving c- straints.Afterafewannualworkshops,CP'95tookplaceinCassis,France;CP'96 in Cambridge, USA; CP'97 in Schloss Hagenberg, Austria; CP'98 in Pisa, Italy and CP'99 in Alexandria, USA. This year the conference is held in Singapore, from 18 through 21 September 2000. This volume comprises the papers that were accepted for presentation at CP2000.From the 101 papersthat were submitted, 31 papers wereaccepted for presentation in the plenary session and 13 papers were selected as posters and have a short version (?
ve pages) in this volume. All papers were subjected to rigorous review three program committee members (or their designated revi- ers) refereed each paper. Decisions were reached following discussions among reviewers and, in some instances, by e-mail consultation of the entire program committee.Ibelievethereaderwill?ndthesearticlestobeofthehighestquality, representing a signi?cant contribution to the ?eld.