A Historical Review of U.S. Contributions to the Atomic Redefinition of the SI Second in 1967

This paper was written to commemorate the 50(th) anniversary of the atomic redefinition of the second in the International System (SI) in 1967. It focuses on the work of individuals and organizations in the United States who made significant contributions to the redefinition of the SI second and helped to establish the era of atomic timekeeping.