["Behavioral Sciences &the Law, EarlyView. ", "\nABSTRACT\nExpert opinion about dangerousness or risk is common at sentencing, criminal commitment proceedings and some types of pretrial detention hearings. This article argues that such evidence must be (1) “material” (logically relevant, empirically generalizable, and epistemologically germane), (2) “probative” (a measure of accuracy, which is heightened when the evidence is from an expert), (3) helpful to the factfinder (through promoting “incremental validity”), and (4) presented in a non‐prejudicial manner (i.e., in a way that minimizes the possibility it will be misused or misinterpreted).\n"]