Consistency is a major issue in user interface design. Although graphical user interfaces have benefited tremendously from a focus on the cognitive aspects of consistency, advances in computer technologies now allow for more socially demanding interfaces incorporating more realistic artificial intelligence agents and new modes of interaction (e.g., voice). This chapter demonstrates that as interfaces become more social, social consistency becomes as important as the more traditional cognitive consistency. This chapter presents experimental studies of humancomputer interaction that are theoretically grounded in social psychology and the computers are social actors (CASA) paradigm. Each study is used to inform design guidelines for social consistency and to open new areas of research on social responses to computers in important areas such as personality, gender, ethnicity, emotion, and the use of "I."