A large literature on the subject of Special Differential Treatment (SDT) has emerged in the last 50 years by both proponents and opponents. The contributions to this volume focus on the rationale, institutional features and economic effectiveness of SDT. The editors have carefully selected a number of key articles with a special emphasis on evaluations of the impact of SDT, especially preferential market access, as well as more recent contributions which discuss whether there is a continued need for such special treatment and how it might be designed both from a development objective and from the perspective of the trading system generally.