Intercrural sex, which is also known as coitus interfemoris, thigh sex, thighing, thighjob and interfemoral sex, is a type of non-penetrative sex in which the penis is placed between the receiving partner's thighs and friction is generated via thrusting. It was a common practice in ancient Greek society prior to the early centuries AD, and was frequently discussed by writers and portrayed in artwork such as vases. It later became subject to sodomy laws and became increasingly seen as contemptible. In the 17th century, intercrural sex was featured in several works of literature and it took cultural prominence, being seen as a part of male-on-male sexual habits following the trial and execution of Mervyn Tuchet, 2nd Earl of Castlehaven, in 1631.

In modern times, intercrural sex is practiced in relationships of various orientations. In Paris, it was commonly performed as a part of prostitution, and in South Africa, was used to combat acquired immunodeficiency syndrome (AIDS); this practice was eventually phased out.

Knowledge of intercrural sex that was extracted from studies and its relationship to AIDS and pregnancy is low. It has been reported as a means of safe sex for human immunodeficiency virus (HIV) positive patients and has a lower risk of infection than sexual intercourse. Studies have found a fluctuating percentage of sexual assault cases have involved intercrural rape, with little to no physical evidence.

Kenneth Dover first introduced the term "intercrural sex" in his 1978 book Greek Homosexuality. Dover used the term to refer to sexual activity between an older man and a young boy. The Ancient Greek term for this practice was διαμηρίζειν diamērizein ("to do [something] between the thighs"). Webster's Dictionary defines intercrural sex as an act in which one partner "plac[es their] penis ... between the other partner's [closed] thighs ... [and thrusts] to create friction". Synonyms include coitus interfemoris, thigh sex and interfemoral sex.

Kang Tchou of Cambridge University notes Dover's definition is similar to the idea of "heavenly love" articulated by Pausanias that "encourages a stable life-long relationship between the boy and the man and enhances the intellectual development of the younger boy".

Intercrural intercourse was a common manifestation of pederasty in ancient Greece; young men were forbidden from having sex with older men in a manner beyond intercrural. It has been associated with Eromenos, although its prominence in such a relationship is undetermined and anal sex may have been more common. Intercrural sex was not exclusively executed by homosexual men; by the early-AD era, it fell out of practice as sex with women became more encouraged in Greek society.

Intercrural sex has been depicted on artworks such as vases, where they were called "courting scenes", and was much discussed by writers. After the 5th century BC, visual depictions of it were sparse and almost exclusively found on black-figure pottery. Zeno of Citium and Aristophanes have been said to reference the act; the latter was the first to document intercrural sex being practiced in a heterosexual capacity. Aeschylus' play Myrmidons features the implication of adult men engaging in the act. Joan Roughgarden refers to intercrural intercourse as the "gay male missionary position" of Ancient Greece.

Historical sodomy laws have included intercrural intercourse within their purview. In 15th-century Italy, it was a part of sodomy's infamous reputation; in renaissance Venice, capital punishment was considered against the partner initiating intercrural sex. Medieval penitentials often highlighted intercrural sex as sinful and gave instructions on ways to repent; early Christianity regarded intercrural intercourse as "more respectable" than anal sex. Islamic jurisprudents considered intercrural sex "reprehensible," although its lesser status led to practitioners avoiding harsh punishments.