Since the publication of the first edition in 1986, the five editions of this work have charted the major evolutions in the law and practice of international arbitra- tion over the last quarter century. In some ways this fifth edition maintains a continuity with the past; in other ways it marks a departure. Those who have grown familiar with the structure, content and style of past edi- tions will recognise much in the new edition. Although two changes have been made to the chapter orders (the chapter on the Agreement to Arbitrate now fol- lows immediately after the introductory chapter, and the chapter on investment treaties now precedes the chapters on challenge and enforcement of awards), the chapters continue to follow (indeed now more logically) the chronological order- ing in which the anatomy of an international arbitration is best understood, taught and practised. The content continues to cover many of the key subjects relevant to the law and practice of international arbitration that appeared in the fourth edition, with some notable new additions that are identified below. And as for style, we have made a determined attempt to retain what many readers tell us is the valued signature of this commentary; a clarity and economy of expression that actively discriminates between notable authorities and repetitive citations.