This is a wide-ranging series, covering a large proportion of Cockcroft's career from his time at university until his death. Retaining Cockcroft's own arrangement, the series has been split into sections including: general correspondence with scientists; correspondence with particular individuals; correspondence arranged by subject; correspondence with and on the numerous people who asked for Cockcroft's help in finding various positions, after the Second World War; miscellaneous papers; and some additional correspondence including material relating to the Cavendish Laboratory in Cambridge.