The doctrines of waiver, variation and estoppel are relied upon to justify or criticize a party's changed position as to its contractual obligations. This book provides a complete practitioner guide to these complex but important doctrines, analysing their basic foundations and their relationship with other areas of law including contract, restitution, and equity. As well as clarifying and explaining these doctrines in relation to other areas it also considers their application in various aspects of commercial law.This new edition provides a thorough analysis of the increasing trend in commercial parties to insert "no waiver" clauses into contracts and considers the behaviour adopted by the courts in relation to these and other matters. It also includes coverage of important cases such as the House of Lords decision in Yeoman v Cobbe, Dallah Real Estate v Pakistan Ministry of Religious Affairs and those such as the Scottish decision in City Inns which demonstrate an on-going confusion and uncertainty in the analysis and application of these doctrines.