Russell J. Hemley and Ho-kwang (David) Mao (both Carnegie Institution of Washington/Carnegie/DOE Alliance Center and the High-Pressure Collaborative Access Team, APS sector 16) are recipients of the 2005 International Balzan Foundation Prize for Mineral Physics. The foundation, which is based in Milan, Italy, made the award “For the impressive impact of their joint work leading to fundamental breakthroughs, theoretical and experimental, in the field of minerals submitted to extreme physical conditions. They have operated as a highly effective team, characterized by twenty years of research contributions at the highest level. They have developed techniques which allow them to study the behaviour of a wide range of materials, such as hydrogen, the most abundant “mineral” in the universe. Their results have deep implications for our understanding of nature.