This chapter discusses classic perception issues, and summarizes some of the approaches taken by social cognition research. Social cognition may be defined as the study of how people understand their social worlds. The field of person perception has deep roots in social psychology; there has been speculation about the perceptions of self and others as long as there has been social analysis. Since the late 1960s, attribution models have, been investigated extensively within social psychology and have been applied to problems not only in social psychology but also in clinical, personality, and developmental psychology. Since the late 1970s social cognition has been dominated by models and approaches largely imported from cognitive psychology. Since the 1980s the traditional areas of person perception have more or less been supplanted by what is called social cognition. Several basic assumptions tend to guide research in social cognition. Social cognition like cognitive psychology generally places a premium on showing that the cognitions are inherently biased.