It is well known that most people who think about suicide do not attempt or die by suicide. Capability for suicide, a construct proposed by Joiner (2005) within the interpersonal theory of suicide, was relatively novel in that it explained a potential mechanism by which individuals move from thinking about suicide to engaging in suicidal behavior. In this paper, we examine Joiner’s (2005) original conceptualization of the nature of capability for suicide, and review the evidence for and against this conceptualization. We examine the evidence for specific constructs that comprise capability for suicide, how capability for suicide develops, whether it can change, and possibilities regarding the functional neural correlates of capability for suicide. We then end our review proposing future directions in the study of capability for suicide, which include research across disciplines and countries.