The majority of the world’s Muslim population (1.6 billion) follows the Sunni branch of Islam, and approximately 10-15% of all Muslims follow the Shiite (Shi’ite, Shi’a, Shia) branch. Shiite populations constitute a majority in Iran, Iraq, Bahrain, and Azerbaijan. There are also significant Shiite populations in Afghanistan, Kuwait, Lebanon, Pakistan, Saudi Arabia, Syria, and Yemen. Sunnis and Shiites share most basic religious tenets. However, their differences sometimes have been the basis for religious intolerance, political infighting, and sectarian violence.
The attached report includes a historical background of the Sunni-Shiite split and discusses the differences in religious beliefs and practices between and within each Islamic sect as well as their similarities.
Islam: Sunnis and Shiites (PDF 5 pages)