Lay theory research on intergroup relations has rapidly grown over the past two decades.Drawing on articles in this Special Issue, we showcase the latest developments.First, we define lay theories, addressing the extent of overlap with scientific theories and differences among lay theories in terms of type of representation, level of articulation, frequency of activation and use, range of applicability, and degree of universality.Second, we describe advances in the understanding of the functions of lay theories.Third, we review the far-reaching implications of lay theories for group and intergroup processes.Fourth, we discuss the movement toward comparing and contrasting related lay theories.Taken together, these articles suggest the study of lay theories provides a fuller understanding of intergroup relations.