Up until recently, research on loyalty and Islam—here considered as the discourses and practices of Muslims in regard to the Muslim tradition—had ignored the topic of loyalty. Interest in loyalty in Islam has just lately grown sufficiently and extensively. This entry is both bibliographical and thematic. It seeks to identify the principal themes that have dominated Muslim loyalty studies for the past thirty years or so. Additionally, it provides a thorough synopsis of over 100 studies on loyalty that were published during the same time span in Arabic and European languages. Allegiance in Muslim political ethics always had more than one connotation and the religious component of loyalty, while not strictly defined, allowed and even justified the overlap of multiple loyalties. A person’s or a family’s, ruler’s, or dynasty’s power to govern an area or defend religious institutions and symbols was intimately linked to the loyalty they could claim. Most studies agree on the diversity of political allegiance in modern Islam with regard to perceptions of religion, ethnicity, self-interest, etc.; it is also co-relative in the sense that it is mixed with other allegiances, such as those of family, tribe, leadership, or country.