Activities and relationships in BDSM are often characterized by the participants' taking on roles that are complementary and involve inequality of power; thus, the idea of informed consent of both the partners is essential.

[21] Often, BDSM contracts are set out in writing to record the formal consent of the parties to the power exchange, stating their common vision of the relationship dynamic.

[4] Sadomasochistic scenes sometimes reach a level that appears more extreme or cruel than other forms of BDSM—for example, when a masochist is brought to tears or is severely bruised—and is occasionally unwelcome at BDSM events or parties.

[citation needed] The terms sadism and masochism are derived from the names of the Marquis de Sade and Leopold von Sacher-Masoch, based on the content of the authors' works.

[citation needed] In 1843, the Ruthenian physician Heinrich Kaan published Psychopathia Sexualis (Psychopathy of Sex), a writing in which he converts the sin conceptions of Christianity into medical diagnoses.

[dubious – discuss] The German psychiatrist Richard von Krafft-Ebing introduced the terms sadism and masochism to the medical community in his work Neue Forschungen auf dem Gebiet der Psychopathia sexualis (New research in the area of Psychopathy of Sex) in 1890.

This led to the first time use of the compound term sado-masochism (German sado-masochismus) by the Viennese psychoanalytic Isidor Isaak Sadger in their work, "Über den sado-masochistischen Komplex" ("Regarding the sadomasochistic complex") in 1913.

At most clubs and group-organized BDSM parties and events, dungeon monitors (DMs) provide an additional safety net for the people playing there, ensuring that house rules are followed and safewords respected.

Using crops, whips, or floggers, the top's fine motor skills and anatomical knowledge can make the difference between a satisfying session for the bottom and a highly unpleasant experience that may even entail severe physical harm.

When a scene takes place in a public setting, it may be because the participants enjoy being watched by others, or because of the equipment available, or because having third parties present adds safety for play partners who have only recently met.

BDSM parties show similarities to ones in the dark culture, being based on a more or less strictly enforced dress code; often clothing made of latex, leather or vinyl/PVC, lycra and so on, emphasizing the body's shape and the primary and secondary sexual characteristics.

This scene appears particularly on the Internet, in publications, and in meetings such as at fetish clubs (like Torture Garden), SM parties, gatherings called munches, and erotic fairs like Venus Berlin.

[86][87][88] The spectrum ranges from couples with no connections to the subculture outside of their bedrooms or homes, without any awareness of the concept of BDSM, playing "tie-me-up-games", to public scenes on St. Andrew's crosses at large events such as the Folsom Street Fair in San Francisco.

In 2003, the media coverage of Jack McGeorge showed that simply participating and working in BDSM support groups poses risks to one's job, even in countries where no law restricts it.

In 1996, the website and mailing list Datenschlag went online in German and English providing the largest bibliography, as well as one of the most extensive historical collections of sources related to BDSM.

Moser's study comes to the conclusion that there is no scientific evidence, which could give reason to refuse members of this group work- or safety certificates, adoption possibilities, custody or other social rights or privileges.

[141] Baumeister found that masochistic males experienced greater: severity of pain, frequency of humiliation (status-loss, degrading, oral), partner infidelity, active participation by other persons, and cross-dressing.

What he found in 2001, was that people in BDSM were open to discussion about the topic of bisexuality and pansexuality and all controversies they bring to the table, but personal biases and issues stood in the way of actively using such labels.

He concluded that the standing of bisexuals in the BDSM and kink community was unchanged, and believed that positive shifts in attitude were moderated by society's changing views towards different sexualities and orientations.

Though there were not enough female respondents to draw a similar conclusion with, the fact that there is a difference in gay and straight men suggests strongly that S/M (and BDSM in general) can not be considered a homogenous phenomenon.

[153] Still, biases and misinformation can result in pathologizing and unintentional harm to clients who identify as sadists and/or masochists and medical professionals who have been trained under older editions of the DSM can be slow to change in their ways of clinical practice.

[89] There has also been research which suggests BDSM can be a beneficial way for victims of sexual assault to deal with their trauma, most notably by Corie Hammers, but this work is limited in scope and, to date, has not undergone empirical testing as a treatment.

The collection of historic texts related to sensuous experiences explicitly emphasizes that impact play, biting and pinching during sexual activities should only be performed consensually since only some women consider such behavior to be joyful.

Flagellation practiced within an erotic setting has been recorded from at least the 1590s evidenced by a John Davies epigram,[167][168] and references to "flogging schools" in Thomas Shadwell's The Virtuoso (1676) and Tim Tell-Troth's Knavery of Astrology (1680).

[173] Other sources give a broader definition, citing BDSM-like behavior in earlier times and other cultures, such as the medieval flagellates and the physical ordeal rituals of some Native American societies.

[177] Alfred Binet first coined the term erotic fetishism in his 1887 book, Du fétichisme dans l'amour[178] Richard von Krafft-Ebing saw BDSM interests as the end of a continuum.

[187][188] One of the works of art is metal bootprints along the curb which honor 28 people (including Steve McEachern, owner of the Catacombs, a gay and lesbian S/M fisting club, and Cynthia Slater, a founder of the Society of Janus, the second oldest BDSM organization in the United States) who were an important part of the leather communities of San Francisco.

Padded handcuffs, latex and leather garments, as well as more exotic items like soft whips for fondling and TENS for erotic electro stimulation, can be found in catalogs aiming at classical vanilla target groups, indicating that former boundaries increasingly seem to shift.

On 1 April 2002, Articles 135 and 197 of the Swiss Criminal Code were tightened to make ownership of "objects or demonstrations [...] which depict sexual acts with violent content" a punishable offense.

[203] Following Operation Spanner, the European Court of Human Rights ruled in January 1999 in Laskey, Jaggard and Brown v. United Kingdom that no violation of Article 8 occurred because the amount of physical or psychological harm that the law allows between any two people, even consenting adults, is to be determined by the jurisdiction the individuals live in, as it is the State's responsibility to balance the concerns of public health and well-being with the amount of control a State should be allowed to exercise over its citizens.