The research studies reported in this book were completed between June, 1976 and November, 1979, with a USPHS research grant (MH- 27849) from the Center for Studies of Crime and Delinquency, National Institute of Mental Health. Every phase of the project was an exercise in combining the research methods of psychology with the concerns of law, legal systems, and legal process. Research psychologists will be especially interested in our efforts to apply psychological constructs and research methods to a difficult decision-making problem in law. This report describes in some detail the project's development of experimental measures of psychological condi- tions related to legal standards and demonstrates the ways in which research design was influenced by concerns of law and the juvenile justice system. Lawyers, judges, and youth advocate groups have already ex- pressed considerable interest in the implications of the project's results for the formation and modification of juvenile law and procedure. In each chapter, I have attempted to describe carefully the ways in which the empirical research results are applicable to these concerns, and I have tried to specify the limits which must be acknowledged in inter- preting the results for application in the legal process.