Half a century of experience with development aid has created crucial questions about what works and what does not in different contexts.Development evaluation is evolving rapidly, both to provide accountability for results and to supply lessons of experience that can improve current development practice. Much is yet to be learned about what methods work best for what evaluation tasks. And, even where methods can be agreed upon, their use is often impeded by institutional and capacity constraints. This volume takes stock of recent progress toward defining and evaluating development effectiveness, with particular emphasis on assessing the potential of new evaluation methodologies.This work includes contributions from a wide range of distinguished academics and practitioners. The authors discuss the difficulty of defining development objectives to be evaluated; the relation between approaches to aid itself and approaches to aid evaluation; problems of evaluating the performance of development agencies; and the relative merits of quantitative, qualitative, and mixed evaluation techniques for judging performance. Several contributors look at how the quality of evaluative evidence can be improved, with particular attention to the potential of randomized experimental approaches. Sustainability and risk, which are critical factors in development effectiveness, are addressed in chapters on institutional aspects of sustainability and the application of Bayesian approaches to identify and mitigate critical risks. Practitioners give insights on building and satisfying demand for evaluation in developing countries and on the use of evaluation findings to improve decision making on development policies and programs.This volume offers useful insights into methods for evaluating the effectiveness of development and assessing the performance of development aid and aid agencies.George Keith Pitman is senior evaluation officer, Sector and Thematic Evaluations, in the Operations Evaluation Department at the World Bank. Osvaldo N. Feinstein is manager, Partnerships and Knowledge Management, in the Operations Evaluation Department at the World Bank, and has published widely on evaluation and development issues. Gregory K. Ingram is director-general, Operations Evaluation, at the World Bank Group.