The research and development (R&D) arm of the Forest Service, U. S. Department of Agriculture (USDA), with approximately 550 researchers in a range of biological, physical, and social science fields, seeks to better understand and describe the complex mechanisms at work in our Nation's forests and grasslands. Research has been part of the Forest Service's mission since the agency's inception in 1905. Today, programs occur in all 50 States, along with U.S. territories and commonwealths. Whether the study is invasive insects, new forest products, or wildlife ecology, the work focuses on informing policy and land-management decisions in order to promote sustainable management of the Nation's diverse forests and rangelands. Researchers work independently and with many partners, including other agencies, academia, nonprofit groups, and industry. This report presents highlights of work conducted in 2006 by Forest Service scientists. The work is organized under seven broad themes: (1) fire, (2) invasive species, (3) outdoor recreation, (4) water and air, (5) resource data and analysis, (6) wildlife and fish, and (7) resource management and use.