This book constitutes the refereed post-conference proceedings of the 15th International Workshop on Groupware: Design, Implementation, and Use, held in Peso da Régua, Douro, Portugal, during September 13-17, 2009. The 30 papers presented were carefully reviewed and selected from numerous submission. The topics covered are mobile collaboration, social aspects of collaboration, technology for CSCW, groupware evaluation, CSCW design, geo collaboration, collaborative learning, and modeling CSCW.