Policy analyses frequently clash. Their disagreements stem from many sources, including models, empirical estimates, and values such as who should have standing and how different criteria should be weighted. We provide a simple taxonomy of disagreement, identifying distinct categories within both the positive and values domains of normative policy analysis. Using disagreements in climate policy to illustrate, we demonstrate how illuminating the structure of disagreement helps to clarify the way forward. We conclude by suggesting a structure for policy analysis that can facilitate assessment, comparison, and debate by laying bare the most likely sources of disagreement. © 2011 by the Association for Public Policy Analysis and Management.