Phase equilibria, chemical reactions, equations of state and elasticity investigated at high P-T in candidate materials for the mantle and the core provide an experimental basis for modelling the structure, dynamics and evolution of the Earth's deep interior. During the past three decades, diamond-anvil cells have been developed for experimental simulation of the pressure conditions of the entire Earth in the laboratory. Simultaneous high temperatures have been generated with various heating techniques. Physical and chemical properties of materials have been determined in situ at high P-T with microsampling techniques. Further improvements in accuracy and versatility of these measurements are essential for resolving key geophysical problems. Some recent developments in our laboratory are summarized, and assessments of the present status and immediate future of the field are offered.