This book constitutes the refereed proceedings of the Third International Workshop on Cooperative Information Systems, CIA'99, held in Uppsala, Sweden in July/August 1999. The 16 revised full papers presented were carefully reviewed and selected from a total of 46 submissions. Also included are ten invited contributions by leading experts. The volume is divided in sections on information discovery and management on the Internet; information agents on the Internet-prototypes systems and applications; communication and collaboration, mobile information agents; rational information agents for electronic business; service mediation and negotiation; and adaptive personal assistance.