The process of making medical decisions used to be straightforward. Clinicians selected the treatment course they determined would best promote the patient’s interests. More recently, in response to increased emphasis on individual autonomy, it is the patient, in consultation with their clinicians and loved ones, who makes medical decisions. This approach respects patients who are able to make their own treatment decisions. However, it poses a challenge for the many adult patients who are unable to understand the information relevant to the decision in question, reason in light of this information and their own values, make a voluntary decision on this basis, or communicate their decision.