My research area is theoretical particle physics. My recent work focuses on deriving rigorous results for hadrons in QCD, the theory of the strong interactions. First principle calculations are difficult in this theory because the Lagrangian description is given in terms of quarks and gluons, not hadrons. Progress has been made by introducing new calculational methods based on approximate symmetries of QCD, such as chiral symmetry and heavy quark spin-flavor symmetry. The most exciting recent development is the use of an expansion in 1/Nc, where Nc is the number of colors, to show that static properties of baryons satisfy light quark spin-flavor symmetry relations to high accuracy. This development explains many of the successes of the phenomenological models, such as the non-relativistic quark model and chiral soliton model, directly in QCD.