This collection of essays underscores the importance of theory in program evaluation and analyzes the nature and implications of theory-driven evaluations. Scholars from different disciplines cover a wide range of issues, such as functions of program theory, the interface between theory and methods, strategies for formulating theory, cost and resource constraints, different types of theory-driven evaluations, and the future implications of such evaluations. This broad-based analysis is designed for interdisciplinary audiences in all the social sciences, including political scientists, sociologists, and public administrators. This policy study analysis points to four types of theory that guide evaluations and describe theory-driven metaevaluation. Five approaches are used to analyze research strategies and methods. Three applications offer insights into programs and policies and their implementation - multigoal theory-driven approaches, programs for the homeless, and children's mental health services. Five chapters examine applications in impact assessment and cost-benefit analysis - the importance of theory in selection modeling, the impact of plant closings, research-based theory for educational planning and evaluation, using meta-analysis in evaluation, and theory-driven approaches to cost-benefit analysis.