The majority of the world's Muslim population 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. Sunnis and Shiites share most basic religious tenets. However, their differences sometimes have been the basis for religious intolerance, political infighting, and sectarian violence. This 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. The report also relates Sunni and Shiite religious beliefs to discussions of terrorism and sectarian violence that may be of interest to Congress.

This report focuses on the United States' relationship with Iran and how the Obama Administration is handling prior administration's economic sanctions against Iran. The Obama Administration's policy approach toward Iran has contrasted with the Bush Administration's by attempting to couple the imposition of sanctions to an active and direct U.S. effort to negotiate with Iran on the nuclear issue. That approach was not initially altered because of the Iranian dispute over its June 12, 2009, elections. However, with subsequent negotiations yielding no firm Iranian agreement to compromise, since early 2010 the Administration has focused on achieving the imposition of additional U.N., U.S., and allied country sanctions whose cumulative effect would be to compel it to accept a nuclear bargain.

This report discusses the reasons that Iran is considered a threat to U.S. security, including Iran's nuclear program, involvement with terrorist organizations, and involvement with neighboring countries' local governments. The report also discusses ways which the U.S. hopes to modify Iran's behavior with sanctions, and the effectiveness of these sanctions.