It is widely accepted that food production benefits from agricultural research, but whether that research benefits the poor is less certain. In 2000, the World Agroforestry Centre and the International Food Policy Research Institute began examining the impact of soil fertility replenishment technologies on the poor in western Kenya. This report is one of seven case studies that comprise a broader IFPRI-managed study designed to determine how agricultural research is benefiting poor people. The goal of this broader study is to identify the conditions under which agricultural research reduces poverty and to improve the targeting of research to the changing needs of the poor. The study develops methods for evaluating the impact of agricultural research on poverty in the context of different agricultural technologies and within different country, social, and institutional settings. It also establishes a foundation that allows agricultural research centers to assess the impact of their work, identify research priorities, and guide technological design to increase future impact on poverty.