Combining rigorous philosophical analysis with a deep knowledge of law, this study of agreements illuminates legal doctrine by philosophical theory and vice versa. Against the prevailing philosophical view of agreements, the book argues that they are to be understood in terms not of promises but of offer and acceptance. Topics covered include the obligations associated with agreements; the practical reasoning that leads parties to make and perform agreements; the relation between agreement and intention; and the reasons the State has to intervene in agreements. There are also separate chapters devoted to doctrines of agreement in the laws of contract, competition and conspiracy.