The slave trade prohibition is among the first recognized and least prosecuted international crimes. Deftly codified in, inter alia, the 1926 Slavery Convention, the 1956 Supplementary Convention, Additional Protocol II to the Geneva Conventions (AP II), the Universal Declaration of Human Rights and the International Covenant on Civil and Political Rights, the norm against the slave trade — the precursor to slavery — stands as a peremptory norm, a crime under customary international law, a humanitarian law prohibition and a non-derogable human right. Acts of the slave trade remain prevalent in armed conflicts, including those committed under the Islamic State of Iraq and al-Shām (ISIS) Caliphate. Despite the slave trade’s continued perpetration and the prohibition’s peremptory status, the crime of the slave trade has fallen into desuetude as an international crime. Precursory conduct to slavery crimes tends to elude legal characterization; therefore, the slave trade fails to be prosecuted and punished as such. Several other factors, including the omission from statutes of modern international judicial mechanisms, may contribute to the slave trade crime’s underutilization. Also, the denomination of human trafficking and sexual slavery as ‘modern slavery’ has lessened its visibility. This article examines potential factual evidence of slave trading and analyses the suggested legal framework that prohibits the slave trade as an international crime. The authors offer that the crime of the slave trade fills an impunity gap, especially in light of recent ISIS-perpetrated harms against the Yazidi in Iraq. Therefore, its revitalization might ensure greater enforcement of one of the oldest core international crimes.