The mantle represents more than 80% of the volume of the Earth. It controls the thermal state of the planet, drives plate tectonics, and is the reservoir from which magmas are extracted. Variations in mantle composition and temperature controls the location and dynamics of volcanoes at the surface of our planet. Using petrology, geochemistry, field work, experimental petrology, and 3-D imaging of mantle-derived rocks, we aim to answer fundamental questions about the nature of the Earth’s mantle.