Edward Appleton attended and contributed papers to the meetings of U.R.S.I. [Union Radio-Scientifique Internationale] from 1927, when he announced his discovery of the F layer at the Second General Assembly in Washington (Coll-37/C.361). He was President of the Union 1934-1952, and also Chairman of the Mixed Commission on the Ionosphere (M.C.I.). The Fourth General Assembly of U.R.S.I. at Copenhagen, to which Appleton contributed a paper on ‘Some Observations on international Research on Atmospherics' (Coll-37/C.361), decided to organise a Sub-Committee to conduct radio observations during the Second Polar Year 1932-1933. Appleton was Chairman of this Sub-Committee and the observations were made at Tromsö in northern Norway. See Coll-37/C.304-C.322 for his journals and photographs of the expedition and correspondence before and after the trip, with colleagues and collaborators on the interpretation and publication of the data. After the Second World War, Appleton, as President of U.R.S.I. and Chairman of M.C.I., helped to organise and attended many of the international conferences and meetings of the Union. See Coll-37/A.83, C.369, H.20, H .36, H.37 for his journey to Australia in 1952 and Coll-37/B.40-B.43 for notes made at that and other meetings. The M.C.I. adopted the proposal of L.V. Berkner for an International Geophysical Year, finally held in 1957-1958, and Appleton helped to foster the preparations. The material, which runs 1927-1961, is presented chronologically and is of varied nature, correspondence, research reports and data, arrangements for meetings and publications, nominations and organisation, etc. The greater part of the correspondence is with the Secretary of M.C. I., W. J. G. Beynon; the correspondence is indexed, but reference should also be made to other letters from Appleton's principal colleagues (Ingram, Beynon, Naismith, Piggott) elsewhere in the collection which deal with or refer to U.R.S.I. affairs. U.R.S.I. reports and papers on various topics of special interest to Appleton are included with related material in other sections of the collection. Drafts and speeches by Appleton at U.R.S.I. meetings or about U.R.S.I. can be found in Section Coll-37/D.