Social cooperation based on reciprocity is the cornerstone of many theories of justice. However, what is central to social cooperation based on reciprocity? How does basing social cooperation on reciprocity structure and constrain theories of justice? In this paper, I consider what is central to reciprocity. I argue that the purpose of reciprocal exchange among persons is important for determining the appropriateness of reciprocal exchanges and that sustaining mutually advantageous relations is not always the point or the only point of reciprocity. This has important implications for theorizing about justice. I show this by outlining two conceptions of justice as reciprocity