Earth’s mantle is compositionally heterogeneous, recording planetary differentiation, core formation, and exchange among deep and surface reservoirs. Understanding its present structure and long-term evolution requires integrating geochemical observations with geophysical constraints. This session welcomes contributions from geochemistry, petrology, mineralogy, geophysics, and geodynamic modelling to investigate mantle composition, heterogeneity, and evolution. Topics include the formation, preservation, and recycling of mantle and crustal reservoirs, evidence for core - mantle interaction, early differentiation, mantle melting as well as links between mantle dynamics and surface processes. We particularly encourage the introduction of new analytical approaches, innovative use of geochemical and geophysical databases, numerical modelling, data-driven methods, and interdisciplinary studies. The session seeks to foster interdisciplinary discussion of how chemical, isotopic, petrological, and geophysical evidence can be jointly used to develop more robust models for the present-day mantle and its evolution through Earth's history.