This chapter provides a comprehensive, evidence-based, and pragmatic overview of forensic and clinical aspects of sexual sadism (SS). This includes conceptual and diagnostic issues, particularly dimensionality and its implications for assessment and diagnosis. Relevant differential diagnoses and comorbidities, including sexual and personality disorders, are considered. The multi-faceted etiology and development of SS is set out, including various biopsychosocial factors of relevance and theoretical models. Prevalence rates in the general population and in those who commit sexual offences and violence are outlined. Then specific groups are considered, including those who commit rape, sexual homicide and child sexual abuse; young, female and non-offending individuals; and those who practice BDSM, highlighting why it should not be conflated with forensically or clinically relevant SS. The chapter then provides practical guidance on assessment, including applying an objective dimensional behavioral scale, the Sexual Sadism Scale (SESAS), to anchor the diagnostic assessment, and important considerations in risk assessment. Recommendations for psychological and pharmacological treatment are made, including considering the impact of working with such individuals on practitioners and systems, before addressing management issues in court, prison or hospital, and the community.