This chapter focuses on the variation in trade flows across country pairs and products as the identification mechanism to detect any trade-inhibiting effect of rules of origin (RoOs). It summarises the existing literature on the analysis of RoOs, stylised facts about association of southeast Asian nation's (ASEAN) RoOs and trade in East Asia and the Pacific, highlighting in particular the prevalence of global value chain in light of recent data on trade in value added. The chapter discusses the econometric analysis and includes an explanation on the data, estimation strategy and results. It reviews the evidence on the effect of ASEAN’s RoOs on preferential trade. There is a prima facie reason to believe that RoOs in the Asia-Pacific region are less susceptible to distortion by special-interest capture than their equivalents in the NAFTA or Paneuro. There are two broad types of RoOs: product-specific rules and regime-wide rules.