The role of science in society is evolving as we enter the 21st century. More than ever before, professional societies, politicians, and others are encouraging scientists to become involved in public policy issues. During the Cold War, many scientists believed that science by itself could solve society's problems. The scientific community is now beginning to realize that many societal issues involve diverse economic, political, social, ethical, and aesthetic values, and rarely, if ever, is single-discipline scientific information alone the basis of public policy that addresses these issues. This reality challenges the scientific community to define a new social contract that is in accord with the social and political conditions that characterize the twilight of the 20th century and the dawn of the 21st century.