Contract Law and Theory, the leading theoretical casebook on contracts, is based on clear, discernible themes and patterns that underlie much of contract law, and as it develops them explicitly, the student is invited to develop a working model of contract law. The model that emerges views contract law through the theoretical lenses of autonomy, efficiency, and pluralism, and asks students to decide if and when these perspectives conflict or converge in contract doctrine. The model is also used throughout as a method for predicting the outcome of contract disputes and is tested through careful case and doctrinal analysis. Contract Law and Theory begins with an overview chapter and many of the following chapters contain introductory essays presenting some of the basic doctrines and theoretical approaches covered in the chapter. The sixth edition adds a new section in Chapter Eight (Mistake and Excuse) that provides a concise overview of recent COVID-related contract litigation, including two new cases and a set of notes describing variations. For professors who cover Chapter Eight in depth, this new section serves to illustrate the contemporary life of the mistake and excuse doctrines. For those who prefer more concise coverage, the section can serve as a stand-alone alternative to the other sections of Chapter Eight, providing professors with the option of introducing, analyzing, and summarizing the law of mistake and excuse in a contemporary context. The book has been carefully edited for accuracy and concision and updated to reflect new scholarly and doctrinal trends, with all main cases remaining substantially the same.