Kleri ni kundi la watu wanaoongoza dini fulani. Jina linatokana na neno la Kigiriki "κλῆρος" - klēros, "bahati", "sudi" au also "urithi". Katika madhehebu mengi ya Ukristo kleri ina daraja takatifu tatu: kuanzia juu ni uaskofu, upadri na ushemasi. Hata hivyo baadhi yao wanapewa pia majina mengine kulingana na huduma zao, kwa mfano: Papa, kardinali, monsinyori, abati, kanoni, arkimandrita n.k. Katika Uislamu hakuna ukuhani, hivyo uongozi unategemea tu elimu ya dini: kuna mufti, imamu, ustadhi n.k. Aston, Nigel. Religion and revolution in France, 1780-1804 (CUA Press, 2000) Bremer, Francis J. Shaping New Englands: Puritan Clergymen in Seventeenth-Century England and New England (Twayne, 1994) Dutt, Sukumar. Buddhist monks and monasteries of India (London: G. Allen and Unwin, 1962) Farriss, Nancy Marguerite. Crown and clergy in colonial Mexico, 1759-1821: The crisis of ecclesiastical privilege (Burns & Oates, 1968) Ferguson, Everett.