Approximately 85% of the matter in the universe is thought to be dark matter. The presence of this mysterious component is well documented in large galaxies, but the amounts of dark matter in galaxies much smaller than the Milky Way are poorly understood. With a new dataset of 100,000 dwarf galaxies, this program will measure their composition and proportion of dark matter, stars, and gas. The principal investigators will also use advanced computer models and simulations to explain the most important physical properties of these dwarf galaxies. This program will develop summer research internships, seminars, and mentoring schemes to increase the retention rates of undergraduate students majoring in physics and astronomy in the States of California, New Jersey, and Ohio. This program will also support research and training opportunities for undergraduate and graduate students in astrophysics. This program will characterize the baryon and dark matter content of massive dwarf galaxies with a united and novel theory and observational approach. This program is made possible by the Merian survey, which is identifying 100,000 well-characterized massive dwarf galaxies. This program will match the internal kinematics of galaxies with their halo mass, using HI line shapes and weak-lensing masses. The principal investigators will use simulations, which successfully reproduce the HI properties of dwarf galaxies, to determine if Cold Dark Matter (CDM) or self-interacting dark matter