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: 1 st – patterns focus on the human user of the system; 2 nd – patterns assist developers in the development process of groupware applications.