BIOLOGICAL RESEARCH has undergone tremendous growth and transformation since 1876, when Robert Koch identified Bacillus anthracis as the causative agent of anthrax, since the structure of DNA was solved in 1953, and even since a “rough draft” of the human genome was completed in February 2001. This expansion of knowledge and the powers it brings shows no signs of slowing, and will undoubtedly bring vast benefits in diagnosing, preventing, and curing disease, and in improving agriculture. However, a plentiful array of the same tools, techniques, and knowledge that have beneficent uses could, if misapplied, be used to destroy human life or agriculture on a mass scale. While it is not a new phenomenon that technologies can have positive and negative consequences, biological science is unique in that its powers over both life and death are profound, and the culture of bioscience is open and relatively available, particularly when compared to nuclear weapons research. In the aftermath of the anthrax attacks of 2001 and the terrorist assaults on the World Trade Towers, policymakers awakened to these inherent powers of biological research and began calling for more governmental controls. The Patriot Act (2001)1 and the Public Health Security and Bioterrorism Preparedness and Response Act of 20022 imposed new regulations on the conduct of research involving “select agents”—the several dozen pathogens that the Centers for Disease Control and Prevention judges to be the most dangerous potential biological weapons. In recent months, the White House Office of Science and Technology Policy has met with representatives of professional science societies, private industry, and others to discuss restricting access to “sensitive homeland security information” generated within government agencies, possibly including data published in scientific journals, lest advances in knowledge and technology inadvertently fuel terrorist attacks using biological weapons. As debate proceeds about whether or how to more closely govern the practice of biological research, it is critical that the profound stakes are understood for both national security and bioscience: a broad scope of research in the life sciences could conceivably be applied towards biological weapons development, but this same research will be essential to creating the medicines, vaccines, and technologies needed to counter the threat of bioterrorism and naturally occurring disease. Efforts to monitor comprehensively all bioscience research that has potentially destructive applications would subsume huge swaths of science, gravely tax civilian research resources, and could discourage scientists from pursuing advances in fields important to medicine and agriculture, fields we urgently need to advance in order to address the grave vulnerabilities currently imposed by bioweapons. The problem of biosecurity in an age of bioterrorism is how to constrain malignant applications of powerful bioscience responsibly without damaging the generation of essential knowledge. Over time, we must construct a network of “checks and balances”: regulations, incentives, cultural expectations and practices that encourage and enable progress in scientific understanding so that knowledge can be brought to bear on human needs, while simultaneously assuring responsible stewardship of powerful knowledge so that it is not used for malevolent purposes. Such stewardship will have to evolve— rapidly, in concert with the pace of advances in the life sciences—to embrace a network of international agreements, legal regulations, professional standards, ethical mores, and catalogues of “best practices” pertinent to