A long tradition of theorizing about the human person holds that the individual self comprises no physical components beyond the boundaries of her body. Recently this view has been challenged by a number of authors, in philosophy as well as biology and the cognitive sciences. These authors have emphasized the myriad of ways in which human thought and behavior are integrated with and depend upon aspects of the environment beyond the boundaries of the organism. Such considerations are taken to imply that the human mental, cognitive, or behavioral system literally extends into the subject's physical environment, to contain elements thereof. I propose to produce a book manuscript in which I argue that (1) in many of the cases found most compelling by advocates of the extended view, there is no theoretical advantage to thinking of human minds as extended and (2) adopting the extended view often detracts from our understanding of human mental capacities and behavior. I will place special emphasis on questions about how best to delineate the systems to which we should attribute consciousness, mental states (such as beliefs), and cognitive capacities (for example, to remember things and to use language). Here I will focus largely on developmental issues, asking how we should explain the genesis of mental phenomena. Interaction with objects in the environment certainly influences development. A plausible account of developmental processes, must, however, attribute historical integrity to the systems whose mental states and capacities are to be explained. This speaks against the inclusion of external objects in the developing system. I will go on to apply this systems-based developmental perspective to questions about mental representation and consciousness. I will also take up the suggestion that a group of individuals can constitute a single mind, asking about the relations between group minds and individual extended minds.