Recent developments in the study of group perception have been guided by four concepts: homogeneity, essentialism, agency, and entitativity. Research on these topics has broadened the scope of questions asked, issues studied, and explanatory mechanisms that are important in the perception of groups. This article summarizes each concept, discusses its contribution to understanding group perception, and highlights unresolved questions that need investigation. Possible conceptual interpretations of the relations among these concepts and their relationship to stereotyping are then discussed. Copyright # 2007 John Wiley & Sons, Ltd.The study of social perception has been a central part of social psychology almost since its very beginnings. The roots of work on impression formation go back to Asch's (1946) seminal paper, ideas about attribution have their origins in Heider's writings (1944), and the empirical study of stereotypes first appeared in the classic study by Katz and Braly (1933). All of these papers appeared in print prior to the time that social psychology was even recognized as a separate subspecialty within the discipline of psychology (Cartwright, 1979).Within the domain of group perception, the focus of course has been on stereotyping: the development, use, and change of people's belief systems about large categories of people defined primarily by gender, race, nationality, religion, occupation, sexual orientation-the list of groups about whom we have stereotypes could go on almost endlessly (Fiske, 1998;Hamilton, 1981;Schneider, 2004). Ever since Allport's (1954) seminal analysis, the important role of categorization has been a central focus of our thinking about stereotypes and stereotyping. Stereotypes are systems of beliefs about categories of people, so questions of how perceivers categorize others into groups are of central relevance to stereotyping. Moreover, the role of categorization in social perception