This article reviews three decades of research on Policy Advisory Systems (PAS), offering a systematic synthesis of its core theoretical propositions and empirical findings. Drawing on the full corpus of academic publications published since the early 1990s, the review examines how PAS scholarship has conceptualised the organisation of policy advice, the actors and resources involved, and their role in the policy process. The analysis traces the development of descriptive and explanatory propositions across institutional, political, and policy contexts, with particular attention to how concepts and analytical dimensions have evolved over time. It also reviews the empirical strategies employed in the literature and assesses how empirical evidence has contributed to theory development and refinement. By integrating theoretical and empirical insights, the review evaluates the cumulative contribution of PAS research and identifies areas of convergence, variation, and unresolved debate. The article concludes by assessing the extent to which PAS scholarship can be understood as a coherent Policy Advisory Framework, and by outlining its analytical scope, limitations, and directions for future research.