政教合一是指政治领袖同时兼为宗教领袖，或者宗教领袖同时兼为政治领袖的政体。

在历史上，一些伊斯兰教国家（如阿拉伯帝国、土耳其帝国）、基督教国家（如拜占庭帝国或亨利八世时代的英国）与古代**（不论独立或从属于中国时），都是典型的政教合一政体。另外，帝国时期的日本是「祭政一致」的国家，天皇为神道教的头号祭司；虽然当时日本政府将神道视为一种「信仰」而非宗教，但实际上等同于政教合一。

Caesaropapism /ˌsiːzəroʊˈpeɪpɪzəm/ is the idea of combining the power of secular government with the religious power, or making it superior to the spiritual authority of the Church; especially concerning the connection of the Church with government. The term caesaropapism (Cäseropapismus) may first have been coined by Justus Henning Böhmer, and was later defined by Max Weber as "a secular, caesaropapist ruler... exercises supreme authority in ecclesiastic matters by virtue of his autonomous legitimacy". According to Weber's political sociology, caesaropapism entails "the complete subordination of priests to secular power."