Written by well-respected experts, this how-to guide provides patterns for the design of human computer human interaction (HCHI). An increasing number of applications are currently designed for use by more than one user, eg: multi-player games, interactive web sites, mobile phones, collaborative learning systems, interactive workspaces and smart environments. In these areas there is a shift from (HCI) human computer interaction to (HCHI) human computer human interaction. The role of patterns in this movement is twofold: 1st -- patterns focus on the human user of the system; 2nd -- patterns assist developers in the development process of groupware applications.