We live in a world of nations, but also one of multi-nation systems. These systems, or transnational regions, affect global economics, politics and diplomacy. Latin America is a widely recognised and documented transnational region. It contains subregional nation systems that might have all of the characteristics and significance of regions and might also affect the broader integration of Latin America. The author defines regionality on the basis of economic integration and measures it with two methods for Latin America, North America, three Latin American subregional systems and one arbitrarily defined nation system within Latin America. He finds a high degree of integration in Latin America, the Andean nations and the Southern Cone of South America. He finds only a modest degree of integration in North America and not significantly greater integration in South America than in Latin America. The division of Latin America into subregions is consistent with the incidence of sub-regional trade initiatives in the past two decades and might be at least partly responsible for the limited progress to date towards Latin America-wide integration. Latin American subregions might now be providing a foundation on which to build regionalism in the future.