Bob is a theoretical nuclear physicist. His primary interests are in nuclear force models, ab initio calculations of light nuclei, and dense nucleon matter and neutron stars. He has led the development of a series of realistic nucleon-nucleon (NN) potentials, including the widely used Argonne v18 potential, that reproduce large amounts of experimental nucleon-nucleon scattering data with high fidelity. He has also helped develop several three-nucleon (3N) potential models of the Urbana and Illinois families. These NN and 3N potentials are used as input to quantum Monte Carlo calculations of nuclear structure and reactions for light nuclei with up to twelve nucleons. They have also been used in variational calculations of dense nucleon matter and neutron stars, including a 1988 prediction that the maximum neutron star mass would be in the range of 2.1 – 2.2 solar masses. More recently these many-body calculations have been extended to study NN and 3N interactions derived within chiral effective field theory.