Mike Gurnis’s innovative work has fundamentally changed the approach to global and regional dynamical studies. His contributions span deep Earth structure, the behavior of subduction zones, plate driving forces, advances in modeling techniques and plate reconstructions, subduction initiation, dynamic topography, continental flooding, and basin sedimentation. The depth and detail with which the conceptual, the technical, the data, and the modeling are treated are hallmarks of his work. Mike Gurnis’s early work provided a paradigm shift in understanding surface processes and basin analysis, shifting the debate over global eustatic changes versus the vertical motion of continents. In a series of influential single-authored papers, he showed that the ridge-spreading model for sea level change failed to conserve mass and eustatic and regional sea level variations had similar amplitudes. Harnessing the power of geological observations, he showed that discrepancies for individual continents were caused by dynamic topography, the deflection of Earth’s surface by mantle flow, ushering in the use of the sedimentary record to study motions in the deep interior. Turning his attention to understanding plate driving forces, Gurnis proved in 2010 that it was possible to model plate boundaries at the kilometer scale while incorporating large-scale variations in rheological properties, achieving an unprecedented match to not only global but also regional plate kinematics by bringing adaptive mesh refinement to mantle convection models. At the same time, he recognized that to complete our understanding, it was necessary to study subduction initiation. With his collaborators, he showed that only a small amount of interplate strain or stress was required to initiate subduction, making them easier to reactivate. Realizing further progress required more data, he turned his attention to gathering them by participating in expeditions and as the driving force behind the South Island Subduction Initiation Experiment. And indeed, they have shown that most Cenozoic subduction zones are reactivated old ones.He exemplifies AGU’s unselfish cooperation in research as the founding director of the Computational Infrastructure for Geodynamics, transforming the delivery and maintenance of open-source software in the geophysics community. He is an underrated mentor. Many former students and postdocs are active researchers and educators. Others, like me, members of an underrepresented group, owe much to his support. Michael Gurnis is a great addition to the Lehmann medalists for his transformative and paradigm-shifting contributions to understanding how mantle dynamics shape Earth's surface and advancing the geophysical computational tools to study it.—Carolina Lithgow-Bertelloni University of California, Los AngelesLos Angeles, California