Challenging orthodox understandings within modern contract law, Discharge of Contractual Obligations provides an innovative doctrinal, historical, and theoretical account of the discharge of contractual obligations. This book delves into a fundamental question: under what circumstances are parties released from their contractual duties for reasons other than performance of those duties? By re-examining cases of breach, frustration, and common mistake -- three key doctrines in modern English contract law -- this monograph demonstrates how these disparate areas of contract law are in fact instances of the discharge of contractual obligations due to a failure of condition. Championing the once-dominant 'failure of condition' model in English law, a straightforward yet groundbreaking explanation for discharge is proposed: ordinarily, parties do not promise to perform 'no matter what, ' but instead make promises that depend on various explicit and implicit conditions. Across ten comprehensive chapters, English explores the theoretical and practical implications of the modern shift to the 'power to terminate' model. Recognising that a wholesale return to the failure of condition model is improbable, the book charts a pragmatic course, illustrating how several practical issues - such as whether a party in breach can terminate due to the other party's breach - are effectively rectified by revitalising this forgotten approach. Written by a leading academic whose contributions to private law have been referenced by courts throughout the Commonwealth - such as the England and Wales High Court (Commercial Court) and the High Court of Australia - this is an essential text for scholars and practitioners of contract law.