Roy Granville McElroy (1907–1994) was a lawyer and politician who held the position of Mayor of Auckland, New Zealand from 1965 to 1968. In this book, which was first published in 1941, McElroy provides a comprehensive analysis of impossibility in relation to contract law, drawing a distinction 'between discharge for physical impossibility or for frustration on the one hand and discharge for failure of consideration on the other'. The text was formed from a manuscript written at Cambridge in 1934, and this manuscript was subsequently edited and updated with new chapters by Glanville Williams prior to publication. An index of cases is included and detailed notes are incorporated throughout. This book will be of value to anyone with an interest in contract law and impossibility as a legal concept.