This chapter assesses regional trade agreements (RTAs). The number of RTAs has grown rapidly since the World Trade Organization (WTO) came into existence in 1995. Roughly one-half of world trade is now conducted within these preferential trade arrangements, the most significant exception to the WTO's principle of non-discrimination. Governments have entered regional economic agreements motivated by a variety of political and economic considerations. They may prefer trade liberalization on a regional rather than a global basis for several reasons. The chapter then reviews the political economy of regionalism: why RTAs are established; which actors are likely to support regional rather than global trade liberalization; the effects that regionalism has had on the trade and welfare of members and non-members; and the relationship between liberalization at the regional and global levels.