Mark Siegler (born June 20, 1941) is an American physician who specialized in internal medicine. He is a leading medical ethicist,[1] and he works at the University of Chicago, where he heads the medical ethics center. He is a fellow at the Hastings Center,[2] and a co-author of Clinical Ethics: A Practical Approach to Ethical Decisions in Clinical Medicine along with Albert R. Jonsen and William J. Winslade.[3]