Ralph Duncan James (8 February 1909 – 19 May 1979) was a Canadian mathematician working on number theory and mathematical analysis.
Born in Liverpool, England, James moved with his parents to Vancouver, British Columbia when he was 10 years old.
Proceeding to University of Chicago, he studied number theory and Waring's problem under L. E. Dickson.
He continued post-graduate study, first with E. T. Bell at California Institute of Technology, then in 1934 with G. H. Hardy at Cambridge University.
He published in the Transactions of the American Mathematical Society and extended some work of Viggo Brun in 1938.