 As soon as he received his Ph.D., he became assistant curator of Roman and Byzantine coins at the American Numismatic Society in New York until 1975, when he was promoted to associate curator, while in 1978 he became deputy chief curator; in 1979 he was promoted to chief curator, following the tenure of Margaret E. Thompson, a position he held until 2000.He is now an honorary curator and life fellow of the American Numismatic Society.He has been a visiting professor at several notable institutions, including Columbia University, Princeton University, University of Padua, Bryn Mawr College, Rutgers University, and New York University.