This paper highlights a major disconnect between the theory and practice of policy design. It provides a contrast between two ways to envisage design in political science. The first focuses on functional requirements and techniques, highlighting what policymakers need to do and the steps they use. The second focuses on theories and empirical studies that situate policy design within the wider study of policy processes, highlighting a major gap between requirements and outcomes. These approaches should complement and inform each other, but rarely do. Most policy theories treat classic descriptions of policy design (such as making policy via series of steps or stages) as divorced from reality, and only useful as ideal-types to contrast with what actually happens. Policy theories may be more accurate, but very few provide equivalent practical lessons (and most do not try). If so, what are the prospects of bringing together these literatures? The paper examines two kinds of theory-informed policy design: theories at the service of analysis or sources of critical analysis and cautionary tales.