Neural engineering technologies—like implanted deep brain stimulators (DBS) and brain-computer interfaces (BCI)—represent exciting and potentially transformative tools for improving human health and well-being. Yet their current use and future prospects raise a variety of ethical and philosophical concerns. Devices that alter brain function invite us to think deeply about a range of ethical concerns—identity, normality, authority, responsibility, privacy and justice. For instance, with a device stimulating my brain, am I still the author of an action (authority)? Should I be held accountable for every action in which a device is operative (responsibility)? Does a device make the interiority of my experience accessible to others (privacy)? Will the device change the way I and others think of myself (identity)? Such fundamental questions arise even when a device is designed for only a relatively circumscribed purpose, such as restoring functioning via a smart prosthetic.