Suicidal ideation is not uncommon in the general population and is even more prevalent in psychiatric samples; however, most individuals who experience ideation will not attempt suicide and even fewer will complete suicide. Despite these discrepancies, the number of studies investigating risk factors for serious suicidal behavior (i.e., attempts and completions) is relatively small. We first review studies in the literature which focus on the distinction between attempted and completed suicide and/or which predict completion status. We then highlight a program of research in our own laboratory which is grounded in Joiners interpersonal-psychological theory of attempted and completed suicide. The theory posits that serious suicidal behavior will not occur unless an individual has both the desire to commit suicide and the ability to do so. Two factors contribute to an individuals desire for suicide, a thwarted sense of belongingness and a sense of perceived burdensomeness on others, while the ability to commit suicide can be acquired over time through habituation to the physical and mental pain involved in self-injury. Finally, we discuss implications of the theory for assessment and treatment of suicidal behavior.