Risk assessment evaluates the potential for certain types of violence (e.g., sex offenses, murder, and domestic violence) among targeted populations of high-risk individuals, such as known offenders. The changing nature of violence risk assessment during the past two decades has been guided by three significant themes. First, traditional monolithic notions of "dangerousness" have been dismantled, and changes have occurred in how risk is defined and communicated. Second, risk assessment has evolved from a focus on one-time risk predictions to an emphasis on the continuous prevention of violence. Third, attempts to increase understanding of the nature of clinical decisions regarding risk have influenced the direction of risk-assessment practices. These influences have fueled a movement toward a middle ground in risk assessment between clinical and actuarial approaches. Professional risk assessments are now framed by both empirical evidence and actuarial tools that are more closely aligned with the clinical decisionmaking process. One section of this chapter examines the application of violence risk-assessment models with two offender populations that have received much attention in the risk-assessment field: sexual offenders and offenders with mental disorders. Summary descriptions are provided for risk-assessment technologies that have been developed for these offender types. In contrast to risk assessment, threat assessment involves instruments or protocols designed to prevent severe violent incidents that engender fear but rarely occur. Selected applications of threat assessment are discussed for school violence and a terrorist attack. Threat assessment is an extension of risk assessment's shift toward applied, management-oriented models for preventing violence. 6 notes and 84 references