In this paper we argue that behind widely accepted problem definitions are myths, stories which draw on tradition and taken for granted knowledge. These myths, which may or may not be true in a factual sense, are important to the definition of problems because they link public issues to widely accepted ways of understanding the world and to shared moral evaluations of conditions, events, and possible solutions to problems.Such myths perform a double-edged function in a policy or planning process. On the one hand, they can provide creative inspiration for policies, a way of translating community values into action proposals, and a powerful means to communicate to a broad public and rally support. They can mediate social and economic change by allowing new policies to carry familiar meaning. On the other hand, a myth can conceal crucial contradictions and realities, legitimize policies that benefit the powerful, and support anachronistic perceptions of policy problems.These ideas are explored in case histories of two areas of urban policy. In one we trace the support for home ownership to a transformation of the Jeffersonian myth of the independent yeoman farmer as the ideal citizen. This use of myth made home ownership the cornerstone of US housing policies and helped suppress alternatives. Though debate over home ownership occurs in the context of housing policy, the tacit purpose is to maintain a myth which is central to our identity as a nation. In the second example, public officials and analysts engaged in an explicit myth-making process to garner support for public-private partnerships as a central tool in urban redevelopment. The myths, which drew on familiar themes, made socially beneficial cooperation seem easy to achieve and legitimized new political and institutional arrangements though it also concealed implementation difficulties.Though myths complicate the effort to use rational, systematic analysis, they are an inevitable part of policy making and planning processes. Planning professionals must openly confront myths and make creative, responsible, use of them rather than allow policies and plans to be subject to their unexamined influence.