The term "crimes against humanity" was first used internationally in the Declaration of France, Great Britain and Russia, made on the 29th of May 1915, to describe the crimes committed against Armenians by the Ottoman government [1]. It was then listed as one of the crimes prosecuted before the International Military Tribunals at Nuremberg and Tokyo [2]. Despite these earlier references, it was decades later that the notion of crimes against humanity was considerably developed and specified with the establishment of international criminal courts, including the ad hoc Tribunals for the former Yugoslavia (ICTY, 1993) and for Rwanda (ICTR, 1994) [3], as well as the Rome Statute (1998) establishing the International Criminal Court [4].
Crimes against humanity have not yet been codified in a dedicated treaty of international law, unlike genocide and war crimes. Since 2014, the International Law Commission has been working on a Convention on the Prevention and Punishment of Crimes against Humanity. A draft of 15 articles was made public in August 2019, including definition of such crimes similar to the ones contained in Article 7 of the Rome Statute (see above) [5].

The Rome Statute is the document that reflects the latest consensus among the international community on the definitions of crimes against humanity. According to the Rome Statute, crimes against humanity mean are of the following acts when committed as part of a widespread or systematic attack directed against any civilian population, with knowledge of the attack: murder, extermination, enslavement, deportation or forcible transfer of population, imprisonment or other severe deprivation of physical liberty, torture, enforced disappearance of persons, apartheid and other inhumane acts of a similar character [6]. Relevant to sexual and gender-based crimes, the Rome Statute codifies the following acts as crimes against humanity: persecution on gender grounds, rape, sexual slavery, enforced prostitution, forced pregnancy, enforced sterilisation and any other form of sexual violence of comparable gravity [7].

Crimes against humanity can be prosecuted at the national level whenever States have incorporated relevant provisions in their domestic laws or simply recognised such crimes as prohibited under national criminal law. Several States have provisions in their domestic legislation that allow the exercise of universal jurisdiction over crimes against humanity [8].

Acts of sexual and gender-based crimes have been prosecuted as crimes against humanity before the ad hoc Tribunals, which significantly developed the international legal framework for holding to account those most responsible for acts of sexual and gender-based crimes, based on the principle of command responsibility. These cases also shed light on the role of military and political leaders who often instigated, encouraged, or oversaw the commission of these acts. Landmark cases include the case against Jean-Paul Akayesu [9] at the ICTR, where the accused was found guilty of rape as a crime against humanity (and as genocide), based on the concept of superior responsibility, given his role in encouraging the commission of these crimes [10].