The materials of this case-book are, in the main, familiar; but they have been organized upon a novel plan. Starting with the medieval actions of debt and covenant, the book traces the evolution of the ideas underlying these two actions through the more flexible action of assumption to the form which they have assumed in modern law. It next deals with the interpretation of both formal and informal contracts, with the remedies of specific performance, damages, and rescission, with the all-pervasive policy against forfeitures, and finally with the methods by which contract obligations may be altered or released. After contracts involving two parties only have been thus examined, the book proceeds to contracts which involve three parties, including promises for the benefit of strangers, assignments, and promises addressed in general terms to persons to be thereafter ascertained. There is a final chapter on illegal contracts. The book was prepared with an eye to the revised curriculum announced in the 1938 catalogue of the Harvard Law School, and with the hope that it would serve as an effective introduction to later courses in the fields of commercial, banking, and insurance law.