This book reports on the productivity impacts of varietal improvement research conducted at a number of international centres affiliated with the Consultative Group on International Agricultural Research. Such centres have been at the forefront of a 40-year effort to breed new varieties of the world's staple food crops. The contributed chapters are the main product of a study initiated and supported by the Impact Assessment and Evaluation Group (now the Standing Panel on Impact Assessment) of the CGIAR. Descriptive data and econometric models have been used to evaluate the impact of research on 11 crops and country case studies in Brazil, China and India. The contents include an introduction and methodology section (3 chapters); crop studies on rice, wheat, maize, sorghum, pearl millet, barley, lentils, potato, cassava, groundnut and common bean (Phaseolus vulgaris); case studies in Brazil, China and India; and a set of 3 synthesis papers reporting global and regional impacts on production and human welfare. The book should prove of significant interest to those working within plant breeding, crop science and agricultural economics.