Interview with Harmon Craig discusses work with Harold Urey's group at the University of Chicago (1941-1955, PhD 1951, Navy service 1944-1946, postdoctoral research 1951-1955); carbon isotope research, C13 and C14; George Callendar's CO2 research; work at the Scripps Institute (1955-2003) with Hans Suess, Roger Revelle; box models; nuclear waste and ocean turnover; helium 3 and 4 in the ocean; boat trip with Niels Bohr; Charles Keeling's CO2 analyses.