This essay provides a conceptual analysis and reconstruction of the notion of mimetic desire, first proposed in Girard (1961). The basic idea behind the idea of mimetic desire is that imitation can play a key role in human motivational processes. Yet mimetic desire is distinguished from related notions such as social modelling and imitation. In episodes of mimetic desire, the process in which the imitative agent's desires are formed is oriented by a particular species of belief about the model or mediator whose desire is copied. These ‘tutelary beliefs’ essential to mimetic desire are distinguished from the ‘thin’ and purely instrumental beliefs about the model central to Bandura's (1986) social cognitive theory and similar models of observational learning. The problem of the identity of the objects of desire in episodes of social modelling motivates a distinction between internal and external forms of interpersonal mediation. Girard's claims about cognitive constraints associated with mimetic desire are examined, and scenarios of reciprocal mimetic modelling are analysed.