PTAs and public international law

Introduction From the first report of the Appellate Body of the World Trade Organisation (WTO) in 1996 to Joost Pauwelyn's seminal work in 2003, commentators and practitioners alike have been grappling with the thorny relationship between the WTO and public international law. More recently, problems in interpreting and applying WTO provisions in the light of customary international law and non-WTO treaties have come to reflect a concern regarding ‘fragmentation’ of international law more generally. One reason for this potential fragmentation lies in the disparate dispute settlement mechanisms under various international legal systems, including preferential trade agreements (PTAs). As negotiations in the Doha Round sputter, and PTAs proliferate, the relationship between PTAs and other institutions and aspects of public international law becomes all the more crucial. States evaluating the benefits of PTAs must be fully aware of the broader international context into which they are born and the implications of international law as each PTA develops. Moreover, existing PTA members may seek additional certainty about their PTA rights and obligations and the likely outcome in the event of a dispute relating to other areas of international law. More broadly, an investigation into the relationship between public international law and PTAs provides an additional case study of the perceived problem of fragmentation of international law. In this chapter, we focus on two primary sources of public international law, namely treaties and customary international law.