The lithosphere-asthenosphere system is fundamental to understanding plate tectonics and the evolution of Earth. Significant advances in geophysical imaging, petrology, rheology, and geodynamics in the past decade have enabled interdisciplinary investigation of the lithosphere-asthenosphere system beneath both continents and oceans in unprecedented detail. Yet, fundamental aspects of the lithosphere-asthenosphere system still remain uncertain, such as the nature and origin of the lithosphere-asthenosphere boundary, the degree of coupling between the lithosphere and asthenosphere, and the thermodynamic state of the upper mantle. We welcome contributions that explore the structure, dynamics, and state of the lithosphere-asthenosphere system across tectonic settings using methodologies including but not limited to seismic and electromagnetic imaging, geochemical modeling, mineral physics, and thermal-mechanical modeling. Interdisciplinary studies that integrate observations across disciplines to jointly constrain the nature of the lithosphere-asthenosphere system are especially encouraged.