The defensibility of the extended mind thesis (EMT) is often thought to hinge on the possibility of extended selves. I argue that the self cannot extend and consider the ramifications of this finding, especially for EMT. After an overview of EMT and the supposed cruciality of the extended self to the defensibility of the former thesis, I outline several lines of argument in support of the possibility of extended selves. Each line of argument appeals to a different account of diachronic personal identity. I argue that no such argument for extended selves succeeds, as no account of diachronic personal identity is both plausible and supports the view that the self can extend. Next, I consider three objections that, if successful, would undercut the preceding argument that the self cannot extend. I conclude by reflecting on the implications of the conclusion that the self cannot extend, including the prospects for EMT.