Indiscernibility and the grounds of identity

Abstract I provide a theory of the metaphysical foundations of identity: an account of what grounds facts of the form a=b a = b. In particular, I defend the claim that indiscernibility grounds identity. This is typically rejected because it is viciously circular; plausible assumptions about the logic of ground entail that the fact that a=b a = b partially grounds itself. The theory I defend is immune to this circularity.