This thesis examines EU trade policy within the context of the relationships which the EU has established with regional organizations in other parts of the world. For many years these interregional relationships have served as mechanisms through which the EU has attempted to achieve broad political and economic cooperation. Until quite recently, however, the issue of reciprocal trade liberalization was not on the interregional agenda in the majority of cases as the EU prioritized multilateralism within the World Trade Organisation (WTO). Since 2006 in particular, however, the EU has implemented a new approach to trade policy which has involved Preferential Trade Agreement (PTA) negotiations being launched with several other regional organizations. This thesis aims to account for this change in approach. I argue that the EU pursuit of PTAs at the interregional level can be explained by the lack of progress which has taken place within multilateral negotiations in conjunction with the increasing spread of PTAs concluded by other major economies. Despite much initial optimism regarding the potential for interregional PTAs, however, few have been successfully concluded. I find that the increasing divergence of preferences among potentially affected domestic interest groups in developed and developing countries which has hindered multilateral agreement in recent years has also served to obstruct the conclusion of interregional PTAs in the majority of cases. The EU, in line with its new competitiveness driven approach to trade policy, has therefore increasingly resorted to bilateral PTA negotiations in order to advance the liberalization agenda. The puzzle is that this has occurred in some cases but not in others. I find that the decision to switch from an interregional to a bilateral approach to trade negotiations in certain cases has closely correlated with the observable expressed preferences of influential business and industry associations within the EU. As such I argue that EU interregional trade policy must be examined within the context of both challenges and opportunities presented by the global economy as well as the preferences of organized domestic interest groups. This thesis presents a comparative case study analysis of the EU’s relationships with four different regional groups – the Association of Southeast Asian Nations (ASEAN), the Comunidad Andina de Naciones (CAN), the Mercado Común del Sur (Mercosur), and Central America. The major aims of the study are to account for the decision to launch PTA negotiations at the interregional level, the low rate of success which has been achieved, and the decision to commence bilateral negotiations in place of an interregional approach in certain cases.