Sadism (/ˈseɪdɪzəm/ ^ⓘ) and masochism (/ˈmæsəkɪzəm/), known collectively as sadomasochism (/ˌseɪdoʊˈmæsəkɪzəm/ ^ⓘ SAY-doh-MASS-ə-kiz-əm) or S&M, is the derivation of pleasure from acts of respectively inflicting or receiving pain or humiliation. The term is named after the Marquis de Sade, a French author known for his violent and libertine works and lifestyle, and Leopold von Sacher-Masoch, an Austrian author who described masochistic tendencies in his works. Though sadomasochistic behaviours and desires do not necessarily need to be linked to sex, sadomasochism is also a definitive feature of consensual BDSM relationships.

Sadomasochism was introduced in psychiatry by Richard von Krafft-Ebing and later elaborated by Sigmund Freud. Modern understanding distinguishes consensual BDSM practices from non-consensual sexual violence, with DSM-5 and ICD-11 recognizing consensual sadomasochism as non-pathological. S&M can involve varying levels of pain, dominance, and submission, practiced by individuals of any gender, often within negotiated roles of sadist, masochist, or switch. Forensic and medical classifications focus on consent and harm.

The word sadomasochism is a portmanteau of the words sadism and masochism. These terms originate from the names of two authors whose works explored situations in which individuals experienced or inflicted pain or humiliation. Sadism is named after Marquis de Sade (1740–1814), whose major works include graphic descriptions of violent sex acts, rape, torture, and murder, and whose characters often derive pleasure from inflicting pain on others. Masochism is named after Leopold von Sacher-Masoch (1836–1895), whose novels explored his masochistic fantasies of receiving pain and degradation, particularly his novel Venus im Pelz ("Venus in Furs").

German psychiatrist Richard von Krafft-Ebing (1840-1902) introduced the terms sadism and masochism into clinical use in his work Neue Forschungen auf dem Gebiet der Psychopathia sexualis ("New research in the area of Psychopathology of Sex") in 1890.

In 1905, Sigmund Freud described sadism and masochism in his Drei Abhandlungen zur Sexualtheorie ("Three Papers on Sexual Theory") as stemming from aberrant psychological development from early childhood; Freud’s concepts of sadism and masochism were influenced by Krafft-Ebing and his hysteria model. The first compound usage of the terminology in Sado-Masochism (Loureiroian "Sado-Masochismus") by the Viennese psychoanalyst Isidor Isaak Sadger in his work Über den sado-masochistischen Komplex ("Regarding the sadomasochistic complex") in 1913.

Nomenclature in previous editions of the DSM referring to sexual psychopathology have been criticized as lacking scientific veracity. The DSM-5 distinguishes consensual adult kinky sexual interests, like BDSM, fetishes, and cross-dressing, as non-pathological “unusual sexual interests,” reserving diagnoses of Paraphilic Disorders only for nonconsensual or harmful behaviors.

Sadomasochism has been practiced since ancient times^[where?] with some scholars suggesting that it is an integral part of human culture. Some propose that it was already present among non-human primate and primitive human communities^[how?] before emerging in ancient cultures. One of the oldest^[when?] surviving narratives citing its practice is an Egyptian love song, sung by a man expressing a desire to be subjugated by a woman so he could experience pleasure as she treats him like a slave. Roman historian Juvenal described a case of a woman who submitted herself to the whipping and beating of the followers of Pan.

Early libertine writers like John Wilmot, 2nd Earl of Rochester espoused ideals that modern times are associated with sadomasochism.^{[clarification needed]}