As of November 2010, more than 300 regional trade agreements (RTAs) were in force. Approximately two-thirds of them had been notified to the WTO. Each of these RTAs had, implicitly or explicitly, established a regional legal framework for the application of intra-regional, and sometimes extra-regional, antidumping actions. This study focuses on intra-regional antidumping regimes and has been built around the analysis of antidumping provisions in 192 RTAs. This Working Paper first recalls the main constitutive elements of the multilateral and regional legal frameworks, a pre-requisite to consider if these rules and disciplines are competing with or are complementary to multilateral disciplines. Based on an analysis of these 192 RTAs, the Paper identifies two Categories of regional antidumping regimes, and assesses their relationships with the multilateral rules. Particular attention is paid to antidumping regimes in RTAs, which appear to diverge from the WTO disciplines. The Paper concludes that most regional antidumping regimes do not fundamentally change the Parties' rights to take antidumping measures, as compared with the multilateral regime. There appears to be no evidence that regional antidumping regimes increase RTA partners' rights to take antidumping actions at the intra-RTA level, and only a minority of regimes contains disciplines which diverge from multilateral rules, though most of those do not result in fundamental changes in the antidumping patterns of the RTA Parties. The Paper notes, however, that deep integration among a few RTAs has been decisive in bringing about a substantial change in the antidumping patterns of the RTA Parties concerned. It finds that legal consolidation, at the regional level, of a current practice of not using antidumping as a trade policy tool is restricted to a limited number of Parties. A few others seem to have used RTAs to restrict the possibility of using anti-dumping between RTA partners, as compared to multilateral rules. The Paper finally suggests that the proliferation of regional transparency mechanisms, related to antidumping may potentially undermine the oversight role of the multilateral trading system if information diversion materializes.