Abstract The Earth is a hot, dynamically evolving planet as shown at the surface either by slow, progressive manifestations (plate motion, continental drift) or more violent ones (earthquakes, volcanoes). Mantle convection, which underlies most geological processes, involves large-scale flow of rocks at high pressure and high temperature. Studying the rheological properties of deep-mantle materials is thus one of the biggest issues in mineral physics. It is also one of the most challenging as most of the deep Earth’s minerals are stable only at high pressure. We now have a broad range of experimental techniques allowing us to cover most of the entire P-T conditions range of the inner Earth. However, the usual methods used for mechanical testing - creep at constant stress, deformation at constant strain rate and stress relaxation - can usually not be achieved under those conditions. Measuring strain and stress is in itself a challenging problem at high pressure. The primary aim of this chapter is to give a rapid overview of the recent advance in the field of experimental deformation of minerals at high pressure. The most traditional experiment consists of applying a confining pressure to a cylindrical sample on to which an independent axial load is superimposed in order to generate differential stresses. The strain rate is usually held constant while the force on the piston is monitored with time and total deformation. Pressure can be applied by means of a gas as in the system designed by Paterson ( Paterson, 1970 ). This apparatus has the great advantage of high accuracy with regard to axial stress