This paper challenges the common assumption that an agreement is an exchange of promises. Proposing that the performance obligations of some typical agreements are simultaneous, interdependent, and unconditional, it argues that no promise-exchange has this structure of obligations. In addition to offering general considerations in support of this claim, it examines various types of promise-exchange, showing that none satisfy the criteria noted. Two forms of conditional promise are distinguished and both forms are discussed. A positive account of agreements as joint (...) decisions founded in a joint commitment is sketched. It is argued that the example agreements represent especially clearly the normative structure of social union. (shrink)