Professor Harrison is a pioneer in the field of thermochronometry and its application to important questions of Earth history. His seminal contributions include: development of analytical methods and interpretive models that reveal continuous thermal and tectonic histories from geologic materials, leading a paradigm shift in our view of the evolution of the Himalayan mountain range, and making breakthrough observations of the earliest phase of Earth history that challenge longstanding conventional wisdom. In the course of his career he has mentored many promising young scientists, influenced national geoscience policy, and made his unique analytical facilities available to hundreds of external users.