This chapter aims to increase awareness of the etiology and appropriate treatment of sexual offending behaviors for individuals with Intellectual and Developmental Disabilities (IDDs). It explores prevalence rates of offending among IDD offenders, examines the empirical literature, and documents risk factors for offenders. Specifically, factors such as cognitive processing speed, learning ability, cognitive fluidity, and communication deficits have been shown to increase the likelihood of sexual misbehavior. Clinical and criminal justice professionals are often ill prepared to provide care and management of sexual offending individuals with the types of disorders. Assessment, through comprehensive screening, is the necessary first step in developing a case management plan and ensuring adequate treatment of individuals with intellectual and developmental disorders. The chapter describes how to reduce recidivism among IDD offenders and then concludes with a discussion on assessment and treatment of IDD offenders.