This chapter will consider two related but independent questions. The first question concerns epidemiology: Is the prevalence of violence to others any higher among people who have a major mental disorder than among people who do not? The second question concerns risk assessment: Among people who have a major mental disorder, how can those who will be violent in the future be distinguished from those who will not? These questions are related because the assumed answer to the first, that the prevalence of violence to others is indeed higher among people who have a major mental disorder than among people who do not, is what often motivates the asking of the second. They are independent because it is possible to be interested in the epidemiological question without being concerned with risk assessment (e.g., in studying the stigma of mental disorder) and possible to be interested in risk assessment without being concerned with epidemiology (e.g., if people with mental disorder are less competent to make decisions than people without it [Grisso & Appelbaum, 1998], interventions based on risk assessments may be justified even if violence was less prevalent among people with mental disorder than among other people). In attempting to answer both of these questions, I will not be exhaustive in my citation of evidence. That has been done elsewhere (Monahan, 1997). Rather, I will focus on what I consider the most important recent (i.e., 1990–2000) research and commentary that bear on these issues.