In this interview, Oscar Wallace (Wally) Greenberg recalls his experiences growing up in New Jersey as the child of Jewish immigrants from Eastern Europe and his accelerated education at Rutgers University and Princeton University, where his advisor was Arthur Wightman. He discusses his dissertation called The Asymptotic Condition in Quantum Field Theory, postdocs at Brandeis with S. S. Schweber and at MIT with Francis Low, and early work on high-energy limits and the general structure of quantum field theory. He reflects on his landmark proposal that quarks have a three-valued charge, later called color, as well as the delayed acceptance of the idea, his prediction of later measurements of the excited states of baryons, and his propensity not to promote his contributions. Greenberg also discusses his acceptance of a position at the University of Maryland, where he would spend most of his career, as well as visiting appointments elsewhere, and he offers anecdotes about his interactions with J. Robert Oppenheimer and Albert Einstein at the Institute for Advanced Study. The interview concludes with discussions of what remains unknown in particle physics and of cosmology as a laboratory with particle energies not available on Earth. A technical addendum to the interview lists 24 of Greenbergs key contributions to physics.