This paper examines the literature on identity within mathematics education published in journals over the past two decades. It analyses the theoretical underpinnings, research methods and definitions of identity, providing a critique rather than a summary of the literature. A total of 188 articles from 85 different journals are reviewed in the sample. This review finds support for common complaints of this research area as lacking in definitions of the concept of identity and suggests that the writing in this topic is at times theoretically incompatible. Furthermore, the work in this field may be coming from two distinct paradigms. Identity may be seen as an action and fit within a sociological frame or it may be seen as an acquisition, fitting within a psychological framing. Defining identity as something we do, as an action, and in particular as performative is promoted in this paper. Finally, suggestions are made for future directions in identity research.