This book explores how policy ideas are spread—or diffused—in an age in which policymaking has become increasingly complex and specialized. Using the concept of enterprise zones as a case study in policy diffusion, Karen Mossberger compares the process of their adoption in Virginia, Indiana, Michigan, New York, and Massachusetts over a twelve-year period. Enterprise zones were first proposed by the Reagan administration as a supply-side effort to reenergize inner cities, and they were eventually embraced by liberals and conservatives alike. They are a compelling example of a policy idea that spread and evolved rapidly. Mossberger describes the information networks and decisionmaking processes in the five states, assessing whether enterprise zones spread opportunistically, as a mere fad, or whether well-informed deliberation preceded their adoption.