William Aird, MD is Professor of Medicine at Harvard Medical School and a practicing hematologist at the Beth Israel Deaconess Medical Center in Boston. He spent 20 years of his career directing an NIH-funded research program in vascular biology, studying the mechanisms underlying phenotypic heterogeneity of the endothelium (for example, what makes endothelial cells in the lung different from those in the heart, and why does it matter). He spent several summers as a seasonal investigator at Mount Desert Island Biological Laboratory, exploring the evolutionary origins of the endothelium, using hagfish as a model organism. Bill published a 1900-page book on Endothelial Biomedicine (Cambridge University Press, 2007) in an effort to synthesize the field and promote the endothelium as a clinically relevant organ. In recent years, he has returned to the bedside, where he is passionate about teaching and clinical medicine. He is committed to helping trainees develop critical thinking skills and build conceptual frameworks for understanding and approaching pathophysiology, with the goal of improving individualized patient care.