Sex offender risk assessment is conducted when an individual is alleged or known to have committed a sexual offence. It involves using the results of a forensic evaluation to gauge the likelihood that an individual will commit a new sexual offence. Sex offender risk assessments can be requested in multiple contexts, and at multiple different stages of the legal proceedings including pre-trial, pre-sentencing, post-conviction, and prior to release. They can inform a wide range of legal decisions such as criminal sentencing, level of community supervision, and mandated treatment (whether in the community or an institutional setting). The primary goal of each of these applications is to reduce the individual’s risk of sexual reoffending and thereby enhance public safety. Sex offender recidivism risk is typically measured by considering sets of static and dynamic risk factors that have an established association with sexual offending or reoffending. Actuarial and structured professional judgement (SPJ) instruments are used to integrate the results of a forensic assessment into an expert opinion regarding a sex offender’s risk of reoffending. Actuarial tools rely on a fixed set of predictor variables and apply a predetermined algorithm to generate a probabilistic estimate of risk, while SPJ instruments rely on the clinician’s judgement to determine the weight accorded to the risk factors identified. In both approaches, as the number of risk factors present increases, the individual’s recidivism risk usually rises. Although many risk factors for sexual reoffending have been identified, the presence of deviant sexual interests and significant antisocial or psychopathic personality traits are among the most well supported. Additionally, it is important to consider protective factors that could reduce the risk of recidivism and might also be the focus of risk-reducing and strength-based interventions. Evaluators should be informed of the ongoing advances in sex offending research, as well as special considerations that arise when evaluating unique offender subgroups such as women, those with intellectual or developmental impairments, and linguistically, ethnically, and culturally diverse individuals.