The interpersonal-psychological theory of suicidal behavior (T. E. Joiner, 2005) proposes that an individual will not die by suicide unless he or she has both the desire to die by suicide and the ability to do so. Three studies test the theory's hypotheses. In Study 1, the interaction of thwarted belongingness and perceived burdensomeness predicted current suicidal ideation. In Study 2, greater levels of acquired capability were found among individuals with greater numbers of past attempts. Results also indicated that painful and provocative experiences significantly predicted acquired capability scores. In Study 3, the interaction of acquired capability and perceived burdensomeness predicted clinician-rated risk for suicidal behavior. Implications for the etiology, assessment, and treatment of suicidal behavior are discussed.