In 2004, an ad hoc committee was charged with preparing this third report examining the most senior S&T appointments to federal government positions and updating the accompanying list of the most urgent S&T presidential appointments. Sufficient changes have occurred since the National Academies 2000 report on presidential appointments including the 2001 terrorist attacks, the anthrax deaths, the reorganization of homeland-security activities in the federal government, new developments in S&T, and concerns about the politicization of S&T decision making and advice to warrant this new edition. In contrast with previous reports on the subject, this one covers not only presidential appointments to top S&T leadership positions but also the appointment of scientists, engineers, and health professionals to serve on federal advisory committees that focus on science-based policy or on the review of research proposals. The committee recognizes that other areas of federal responsibility are as important as S&T, but S&T appointments are the only ones within its purview.