This book is the first ever comprehensive analysis of the scope and role of the exemption clause in Article 80 of the International Sales Convention (CISG). The book accounts for the historical background of Article 80, the relation to other provisions (Articles 77 and 79), the underlying principles and the connection to good faith, and argues that the provision is an expression of the duty to cooperate. Furthermore, the conditions for applying the exemption rule and the legal consequences of application are clarified to the benefit of any practitioner. A chapter on homeward trends points out some of the challenges that Article 80 poses to international uniformity. Extensive comparisons to UPICC and PECL are carried out. The book is relevant to scholars, adjudicators and practitioners alike.