This case study explores the development, dissemination, adoption, and impact of improved tree fallows in rural western Kenya. The processes of technology development and dissemination throughout the region are described and analyzed. To analyze adoption and impact, the paper applies a variety of different data collection methods as well as samples from both pilot areas where researchers maintained a significant presence and non-pilot areas where farmers learned of the technologies through other channels. Sample sizes for the quantitative analysis ranged from almost 2,000 households for measuring the adoption process to just over 100 households for measuring impact indicators. Qualitative methods included long-term case studies for 40 households and focus group discussions involving 16 different groups. The paper describes the ways in which farmers used and modified improved fallow practices. Discussion also examines the types of households using fallows and benefiting from their use. Empirical results suggest that improved fallows almost always double on-farm maize yields. In addition, the data indicates that poor households use improved fallows at much greater rate (about 30 percent) than they do fertilizer (8 percent), though, on average, the size of fallow plots remains small, at 440m2. As a result, despite these promising signs, the improved fallow systems were not found to be linked to improved household level food security or poverty indicators primarily, primarily because the size of the fields under the agroforestry systems was on average, quite small.