The requirement that doctors obtain valid consent from patients before providing medical treatment has long been ingrained in both legal doctrine and medical ethics. We summarize the foundations of the informed consent doctrine and discuss the recent evolution in thinking about consent and medical decision making. We show how consent has evolved from physicians merely providing patients information to shared decision making between patients and physicians. We then address three specific examples of situations common in neurological practice that pose challenges in obtaining valid consent: the administration of intravenous tPA following ischemic stroke, consideration of carotid endarterectomy for carotid artery stenosis, and implementation of do-not-resuscitate orders.