This chapter presents an overview of major theoretical policy network developments, disputes, and alternative models, as well as key research results. Taking a chronological approach, the first section identifies the origins of policy network research in studies of power structures and interlocking directorates. The next section examines theories of policy networks constructed on both sides of the Atlantic in the late twentieth century. The third section looks at recent policy network developments, including the emergence of global networks and applications of new theories and advanced statistical methods to policy network research. The chapter concludes that the field has greatly matured as a multidisciplinary specialty and become more institutionalized in recent years. Although it still lacks cohesion around a core set of innovative ideas that could facilitate greater integration, opportunities await for creative analysts to propose paradigms that could take policy network studies in surprising new directions.