 Decisional capacity can be defined as the ability of subjects to make their own medical decisions. Somewhat similar questions of capacity arise in other contexts, such as capacity to stand trial in a court of law and the ability to make decisions that relate to personal care and finances. However, the history behind the more general legal notions of capacity to stand trial and capacity to manage one’s life is different and operates somewhat differently in law (Roth, Meisel, &amp; Litz 1977; Zapf &amp; Roesch 2005). For the purposes of this discussion the notion of decisional capacity will be limited to medical contexts only; most notably, those where decisions to consent or to refuse treatment or participation in clinical research are concerned.