Sunni-Shi'i relations have undergone significant transformations in recent decades. The 1979 Islamic revolution in Iran had a major spill-over effect on the entire Middle East, and the 2003 war in Iraq transformed the Shi'is into the dominant force in Iraq. The emergence of Iran as a regional power following Saddam Husayn's removal, along with the weakness of the Arab state system, raised the specter of the "Shi'i Crescent" threatening Sunni-Arab domination in the region. The present volume demonstrates the complexity of Sunni-Shi'i relations by analyzing political, ideological, and social encounters between the two communities from early Islamic history to the present. While analyzing specific case studies in various Middle Eastern regions, the book provides a panoramic picture ranging from hostility to efforts of cooperation and ecumenism.