This important monograph summarizes, rethinks, and extends a decade of the author's work on therole assignments - the ways in which the roles implied by verbs of a given type play out in terms of position and other syntactic functions. The study of theta roles and the locality of theta-role assignment leads into many interesting areas of linguistic theory, such as scope, the ECP, X-bar theory, binding theory, and the weak crossover condition; Williams's reconstruction thus offers a systematic integration of a remarkably wide range of syntactic phenomena.