Cofounder of the Hastings Center in 1969, Callahan is widely known for his innovative studies in biomedical ethics. His interest in philosophy led him to the moral issues in medicine and rapidly changing technology—and the need for an organization that could engage in the study of such issues. Callahan served as president of the Hastings Center for more than 25 years and now is the senior research scholar and president emeritus. He also is the co-director of the Yale-Hastings Program in Ethics and Health Policy. In addition to serving as a member of several committees, such as the Institute of Medicine and HHS, Callahan also has authored more than 40 books.