Surprisingly little theoretical attention has been devoted to the final step of the public policy implementation chain: understanding why the targets of public policies do or do not “comply” — that is, behave in ways that are consistent with the objectives of the policy. This paper focuses on why program “targets” frequently fail to act in the way that program designers intended and wanted, even when it appears to be in their self-interest to do so. This is a question that can be asked for a broad array of government policies. The paper begins by briefly defining target compliance and the main approaches that governments may use to secure compliance. It then discusses the dominant theoretical approaches to understanding target compliance, and develops a general categorization of reasons for compliance or non-compliance and strategies that are generally used to cope with each of these causes. Finally, the author suggests some lessons about what program designers and implementers should do to address problems of policy non-compliance.