Ioan Mackenzie James FRS (born 23 May 1928) is a British mathematician working in the field of topology particularly in homotopy theory. James was born in Croydon, Surrey, England, and was educated at St Paul's School, London and Queen's College, Oxford. In 1953 he earned a D. Phil. from the University of Oxford for his thesis entitled Some problems in algebraic topology, written under the direction of J. H. C. Whitehead.