The recent financial crisis has questioned whether existing contracts may be adapted, terminated or renegotiated as a result of unexpected circumstances. The question is not a new one. In medieval times the notion of clausula rebus sic stantibus was developed to cope with such situations, and Germany introduced the theory of Wegfall der Gesch‰ftsgrundlage. In England, the Coronation cases provided one possible answer. This comparative study explores the possibility of classifying jurisdictions as 'open' or 'closed' in this regard.