In the present writing, the three main and well-known theories of Imamate (Imami thory, Zaydi theory, and Isma’ili theory) have been introduced and the relations between the three have been discussed. It has been said that, putting emphasis on the Batini meaning for Imamate, Isma’ili theory brings Imamate near to extremism; and, on the other hand, weakening Infallibility and replacing special knowledge by Ijtihd, Zaidis make themselves influenced by Sunni view. Then, the historical development of Imami theory has been discussed and four theories of theologians, muhaddithun, philosophers, and mystics have been explained. It is argued that there is no theoretical explanation with Muhaddithun. The author expresses his hope that this important task may be performed in more dissertations, articles, and writings.