The Kiyotaki and Wright model (1989) of money as a medium of exchange is analyzed within an evolutionary framework. It is shown that fundamental, speculative, and polymorphic states can all be stable, and that there may exist a multiplicity of stable states. Stringent assumptions regarding information and rationality are therefore unnecessary in order to explain the use of money as a medium of exchange, even when the existence of a stable medium requires some individuals to trade their production good for one with a higher storage cost, or when otherwise identical individuals must adopt different exchange strategies.