People's diets can serve as a basis for social identity, and the papers in this special issue examine the social psychological implications of vegetarianism as a social identity. The papers run the gamut from examining how vegetarians are viewed by the omnivorous majority to examining interventions designed to reduce meat consumption. In this paper I provide background information to provide a context for understanding the articles. This information includes a discussion of definitions of vegetarianism, people's motives for adopting a vegetarian diet, and some of the individual differences other than diet that distinguish vegetarians and non-vegetarians.