Doppelgänger is a term drawn from the writing of Jean Paul Richter in his novel Siebenkäs. This term is examined and discussed in this chapter. It stands for the possibility of the existence of a double of a living person and therefore raises questions about the nature of the self and of mind too. The concepts of self and mind are explored and the implications for philosophy of mind are examined. The importance of attending to the empirical literature rather than using thought experiments is emphasized.