This dossier invites the Journal of Borderlands Studies (JBS) readership to explore Southern Common Market (Mercosur in Spanish and Mercosul in Portuguese-Brazilian) borders and border spaces. During the second half of the 1980s, Brazil and Argentina start negotiations related to regional integration. These talks shortly result in the foundation of the Mercosur. Thus, in 1991, Argentina and Brazil, along with Paraguay and Uruguay, sign the Mercosur founding treaty, the Treaty of Asuncion, with the ultimate objective of creating a common market. In order to achieve this goal, the Mercosur member states consider that a free trade area and a customs union need to be established, as well as the four freedoms of a common market, i.e. free movement of goods, services, persons and capital (Article 1). Subsequent treaties amend and consolidate this initial agreement. Nevertheless, the original proposed schedule (1991-1994) cannot be completed, confining the Mercosur to a free trade area with an imperfect customs union. However, these international treaties do not limit the Mercosur to a free trade bloc: the institutions of the Mercosur also reveal an intergovernmental organization that coordinates joint macroeconomic and sectoral public policies, implying a community integration purpose (Vervaele 2005, 390-391). Due to this dual facet, the enlargement and deepening of the Mercosur is progressing in several ways. First, neighbouring countries are linked to the Mercosur, as future permanent members (Bolivia and Venezuela), as associate members (Chile, Peru, Colombia and Ecuador), or as observer (Mexico). Second, agreements are signed with third parties, e.g. a free trade agreement with Israel in 2007. Third, institutions are reinforced, for instance through the creation of a permanent dispute resolution mechanism in 2002; besides, members of the Parliament of the Mercosur will be directly elected for the first time in 2010. Finally, in order to counterbalance the asymmetries of the bloc, the Mercosur members create in 2005 a structural fund, known as the Fondo para la Convergencia Estructural del Mercosur (FOCEM).