William G. Kaelin Jr., MD, is a 2019 Nobel Prize recipient in Medicine or Physiology. He received his MD from Duke University in 1982 and was a house officer and chief resident in internal medicine at Johns Hopkins Hospital. Kaelin was a Medical Oncology Clinical Fellow at Dana-Farber and a postdoctoral fellow in the laboratory of David Livingston, MD, where he began his studies of tumor suppressor proteins. He became an independent investigator at Dana-Farber in 1992, and a Howard Hughes Medical Institute Investigator and Professor of Medicine at Harvard Medical School in 2002. The 2019 Nobel was awarded jointly to Kaelin, Sir Peter J. Ratcliffe, and Gregg L. Semenza for their discoveries of how cells sense and adapt to oxygen availability.