The prediction of dangerous and/or violent behavior is particularly important to the conduct of the U.S. criminal justice system when it makes decisions about restrictions of personal freedom, such as preventive detention, forensic commitment, parole, and in some states such as Texas, when to permit an execution to proceed of an individual found guilty of a capital crime. This article discusses the prediction of dangerous behavior both through clinical judgment and actuarial assessment. The general conclusion drawn is that for both clinical and actuarial prediction of dangerous behavior, we are far from a level of accuracy that could justify routine use. To support this later negative assessment, two topic areas are emphasized: (1) the MacArthur Study of Mental Disorder and Violence, including the actuarial instrument developed as part of this project (the Classification of Violence Risk), along with all the data collected that helped develop the instrument; and (2) the U.S. Supreme Court case of "Barefoot v. Estelle" (1983) and the American Psychiatric Association "friend of the court" brief on the (in)accuracy of clinical prediction for the commission of future violence. Although now three decades old, "Barefoot v. Estelle" is still the controlling Supreme Court opinion regarding the prediction of future dangerous behavior and the imposition of the death penalty in states, such as Texas; for example, see "Coble v. Texas" (2011) and the Supreme Court denial of certiorari in that case.