This study discusses the status of economic integration of the six Gulf Cooperation Council (GCC) countries among themselves, with the larger Middle East and North Africa (MENA) region and globally. It also assesses the main challenges to further integration. The GCC is the most advanced example of sub regional integration in the MENA region, and its objectives are among the most ambitious in the developing world. It has evolved well beyond a focus on free trade in goods to embrace high levels of cross-national labor and capital mobility, and the progressive opening of many sectors within each economy to all member states. The GCC has made good progress on regional integration since its establishment in 1981. Integration efforts have gained considerable momentum following the ratification of the Unified economic agreement in 2001, the signing of the customs union agreement in 2003, and the adoption of the common market agreement in 2008. Under the customs union agreement, member countries have eliminated intraregional tariffs, unified external tariffs, and eased trade restrictions, bringing about a notable increase in the value of goods traded among member states.