Preferential trade agreements (PTAs) have been proliferating for more than two decades, with the negotiations for a Transatlantic Trade and Investment Partnership and a Trans-Pacific Partnership being just the tip of the iceberg. This volume addresses some of the most pressing issues related to the surge of these agreements. It includes chapters written by leading political scientists, economists and lawyers which theoretically and empirically advance our understanding of trade agreements. The key theme is that PTAs vary widely in terms of design. The authors provide explanations as to why we see these differences in design and whether and how these differences matter in practice. The tools for understanding the purposes and effects of PTAs that are offered will guide future research and inform practitioners and trade policy experts about progress in the scientific enquiry into PTAs.