Identity is a core psychological construct: a way of describing an individual that locates him or her within a social and political context. It has become an increasingly prominent topic in psychology, and one with clear relevance to environmental attitudes and behaviors. But definitions of identity and of the role of the natural environment in identity remain imprecise, just as attempts to include measures of identity in environmental research have proliferated. This chapter will discuss the psychological construct of identity and describe how it is relevant to the natural environment. I review research that has directly or indirectly addressed environmental identity, and that has shown the importance of identity in predicting behavior. I conclude with a call for further research that is clearly grounded in theory about identity, as well as research on the ways in which societies and environments can facilitate a strong environmental identity.