||This documet-contains the proceedings of an international conference on impact assessment research held in San Jose, Costa Rica, from 4-7 February 2002. Co-organized by the Economics Program of the International Maize and Wheat Improvement Center (CIMMYT) and the Standing Panel on Impact Assessment (SPIA) of the Consultative Group on International Agricultural Research (CGIAR), the conference was attended by approximately 150 impact assessment practitioners and users. Participants included representatives from CGIAR Centers, national agricultural research organizations, public and private universities, multilaterallending organizations, development assistance agencies, non-governmental organizations (NGOs), philanthropic foundations, private corporations, and the media. The goal of the conference was to examine why many impact assessment studies have had lirnited influence on the way that agricultural research is conducted and have failed to ensure adequate and sustainable financial support for research. Participants concluded that the success of future impact assessment studies could be improved by: (1) better matching impact assessment results to the needs of decision makers; (2) making impact assessments more credible and more understandable, without losing rigor; and (3) improving methods for assessing a broader array of impacts, beyond traditional econornic measures.