Seismological studies give us a high-definition 3-D picture of the Earth's interior in terms of seismic velocity and density. Near the surface, observations of these properties can be compared with rock samples. As we go deeper into the Earth, interpretation of seismic data is more difficult. Laboratory measurements of velocities and other elastic properties of minerals are the key to understanding this seismic information, allowing us to translate it into quantities such as chemical composition, mineralogy, temperature, and preferred orientation of minerals. Here we present a description of modern techniques for measuring elastic properties at high pressures and temperatures, emphasizing those most relevant to understanding the interior of the Earth and other planets.