This book constitutes the refereed proceedings of the Third International Conference on Principles and Practice of Constraint Programming, CP'97, held in Linz, Austria in October/November 1997. The volume presents 37 revised full papers carefully selected from a total of 132 submissions; also included are the abstracts of two invited talks and three tutorials. The papers address all current aspects of constraint programming. Among the topics covered are constraint matching, constraint languages, set constraints, constraint search, constraint satisfaction problems, scheduling, constraint routing, temporal constraints, constraint graphs, local search, object-oriented constraint programming, etc.