Joel Primack’s research has mainly been in relativistic quantum field theory and in cosmology and particle astrophysics, a field that he has helped to create. In collaboration with UCSC astronomers George Blumenthal and Sandra Faber and others, he developed the “cold dark matter” (CDM) theory, which has helped to set the agenda for theoretical and observational cosmology for two decades. More recently, he has been using the largest supercomputers as well as analytic and semi-analytic techniques to investigate the implications of various hypotheses regarding the identity of the dark matter for the formation and distribution of galaxies. He also works on science and technology policy and on the cultural implications of the ongoing revolution in cosmology. In the 1970s, Primack helped to create what is now called the Standard Model of particle physics; for example, in 1972, with Ben Lee and Sam Trieman, he did the first calculation of the mass of the charmed quark using renormalizable electroweak theory. His recent research has concentrated on the nature of the dark matter that comprises most of the mass in the universe. He and Heinz Pagels were the first to suggest that the dark matter might be the lightest supersymmetric partner particle. He also investigated the possibility that some of the dark matter might be light neutrinos (hot dark matter). He and his students and other collaborators have analyzed many variants of CDM—especially CDM with less than a critical density of matter and a compensating cosmological constant (CDM)—and confronted the predictions of these models with a wide range of observational data.