Mark M. Davis, Ph.D. is well known for identifying the first T-cell receptor genes, which are responsible for T lymphocytes ability to “see” foreign entities, solving a major mystery in immunology at that time. He and his research group have made many subsequent discoveries about this type of molecule, subsequently, specifically concerning its biochemical properties and other characteristics, including the demonstration that T cells are able to detect and respond to even a single molecule of their ligand-fragments of antigens bound to Major Histocompatibility Complex cell surface molecules. He also developed a novel way of labeling specific T lymphocytes according to the molecules that they recognize, and this procedure is now an important method in many clinical and basic studies of T cell activity, from new vaccines against cancer to identifying “rogue” T cells in autoimmunity. In recent years his has increasingly focused on understanding the human immune system, from developing broad ‘systems” approaches to inventing new methods to help unravel the complexities of T cell responses to cancer, autoimmunity and infectious diseases.