The world of Islam divides into two main sects with different theological approaches to God that vary at key points in doctrine. The American experience in Iraq since 2003 has spotlighted these key differences, yet few understand their origins. Most works, even those by specialists, construe the division as reaching back to the early formative years of Islam-which it does in some respects-but many do not realize how long it took for the important differences between what became known as Sunni and Shi'i Islam to become solid and fixed as they now seem to be. In other words, in the first few centuries of Islamic history,the term Shi'ism can only be applied retrospectively to a diversity of political sects and religious movements, many of which had little in common.1 Here, a closer analysis of Islamic history from the time of the Prophet Muhammad (570 to 632 C.E.) to the Abbasid Revolution (750 C.E.) will show that there was a diversity of Shi'ite movements throughout early Islamic history and no clear line that divided Sunna and Shi'a in early Islam