This article aims to compare the different conceptions of holy war in Islam and Christianity by way of its depiction by Muslim sources, and to examine if the Islamic context would have conceived of a war carried out by Christians, and therefore infidels, as a holy one. This leads to analysis of whether the Islamic idea of holy war could be understood as a transcultural one or if, on the contrary, its sole conception was limited to those actions carried out by Muslims. To that end, Ibn Khaldūn’s (d. 1406) Kitāb al-‘Ibar will be used as a case study, in which his famous Muqaddima serves as its introduction. The choice of this source is based on two considerations: it is one of the most important and influential historiographical works of the Islamic world; and Ibn Khaldūn maintains a universalist vision of history and its processes, and therefore specifically aims to be cross-cultural.