In this paper we shall argue that mentalistic action explanations, which form an essential component of a mature theory of mind, are conceptually and developmentally derived from an earlier and purely teleological interpretational system present in infancy. First we summarize our evidence demonstrating teleological action explanations in one-year-olds. Then we shall briefly contrast the structure of teleological vs. causal mentalistic action explanations and outline four logical possibilities concerning the nature of the developmental relationship between them. We shall argue for the view that causal mentalistic action explanations are constructed as useful theoretical extensions of the earlier, purely teleological, nonmentalistic interpretational stance.