His research is situated in the intersection of combinatorics, geometry, and number theory; he is particularly fond of counting integer points in polyhedra and the application of these enumeration functions to various combinatorial and number-theoretic topics and problems. He (co-)authored two books and many research papers, more than a third of which feature student coauthors. He has mentored numerous research students at SF State, UC Berkeley, and UC Davis, directs the NSF-sponsored (CM)^2 GK-12 program at SF State, and is one of the codirectors of the San Francisco Math Circle.