Investment in energy research and development in the U.S. is declining despite calls for an enhancement of the nation's capacity for innovation to address environmental, geopolitical, and macroeconomic concerns. We examine investments in research and development in the energy sector, and observe broad-based declines in funding since the mid-1990s. The large reductions in investment by the private sector should be a particular area of concern for policy makers. Multiple measures of patenting activity reveal widespread declines in innovative activity that are correlated with research and development (R&D) investment-notably in the environmentally significant wind and solar areas. Trends in venture capital investment and fuel cell innovation are two promising cases that run counter to the overall trends in the sector. We draw on prior work on the optimal level of energy R&D to identify a range of values which would be adequate to address energy-related concerns. Comparing simple scenarios based on this range to past public R&D programs and industry investment data indicates that a five to ten-fold increase in energy R&D investment is both warranted and feasible. (c) 2006 Elsevier Ltd. All rights reserved.