The Economic Assessment Office of the Advanced Technology Program (ATP) measures the economic impact of co-funding projects with the private sector to develop high-risk, enabling technologies, and seeks to increase understanding of the underlying relationships between technological innovation and economic phenomena. The National Academy of Sciences has praised ATP's evaluation program as "one of the most rigorous and intensive efforts of any U.S. technology program" (National Research Council, 2001). ATP's evaluation efforts were instituted to meet external requests for ATP program results, to use evaluation as a management tool to meet program goals and improve program effectiveness, to understand ATP's contribution to the U.S. innovation system, and to develop innovative methodologies to measure the impact of public R&D investment. To do this, ATP economists track progress throughout each project's life and into the post-project period by conducting surveys, compiling data, producing statistical analyses, undertaking economic studies, and commissioning studies with consultants and research economists. This paper describes the evolution of ATP's evaluation activities, its evaluation best practices based on ATP's experience since 1990, and findings from ATP studies.