The nature of the lithosphere-asthenosphere boundary is critical to understanding the geodynamic and geochemical evolution of Earth, yet its definition is still controversial. In this Symposium we aim bring together experts in seismic methods, magnetotellurics, and potential-field analysis, mantle geochemistry, and numerical modelling of dynamic processes in the Earth to investigate how the lithosphere and underlying mantle have behaved through time. Integrating information from these different types of datasets, will advance discussion of the constraints that help us elucidate the character and location of the lithosphere-asthenosphere boundary in the present-day and older Earth.