This book constitutes the refereed proceedings of the Second International Conference on Principles and Practice of Constraint Programming, CP '96, held in Cambridge, MA, USA in August 1996. The 36 revised full papers presented in the volume were selected from over 100 submissions; also included are abstracts of 22 selected poster presentations and 3 special lectures. CP is the flagship conference series on constraint processing with a number of satellite activities; thus the volume reflects the state of the art in the field.