JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Springer is collaborating with JSTOR to digitize, preserve and extend access to Law and Human Behavior.http://www.jstor.org From its inception, research in "law and psychology" has had an explicitly applied focus. In large part, psychologists have studied legal issues and participated as experts in the legal process in order to improve law and enhance the quality of its justice. This article examines whether and how this can be done. A taxonomy of relationships between the two disciplines is presented which characterizes law and psychology research in terms of its potential for legal change. The use of psychology to effect legal change requires a bringing together of both psychological and legal paradigms. But important differences exist between the styles and methods of reasoning, proof, and justification in psychology and law. The implications of those differences for the use of psychological data in legal change efforts are developed, as are other aspects of "legalism" that may hinder or impede the effectiveness of psychologically oriented law reform. Finally, limitations of a "factual jurisprudence" that derive from the nature of psychological data are examined.