The September 11, 2001, attack on the World Trade Center and the subsequent mailing of letters containing B. anthracis sparked a major expansion of efforts to protect the United States and the international community against bioterrorism. These endeavors, which involve multiple government agencies, academic institutions, nongovernmental organizations, and international organizations, as well as the scientific community, focus on the accelerated advancement of bioscience as a dual-use instrument for both unprecedented good and destructive opportunity. Although fundamental in the practice of science, values such as integrity, honesty, openness, and collaboration are challenged by the potential impact of biodefense applications. More broadly, life scientists are being challenged to consider the possible negative applications of research intended for beneficial purposes and their responsibilities to help reduce the risks of misuse -- a role with which the life sciences community has little recent experience. In this climate of uncertainty and precaution, ethical deliberations are more important than ever. This symposium will highlight the historical roots of concerns about dual-use research in the 20th century, discuss nuclear physics as an example of civic engagement by scientists, focus on current tenets of responsible conduct of research that are relevant to dual-use issues, and consider the implications of expanded biodefense research in the context of international collaborations.