Includes the names and addresses of several of the individuals discussed by Lester in the diaries and those he was in correspondence with during the period.

This diary is blank apart from a handwritten note on the very last page ['Rev. Fr. Victor Dillard, French Jesuit, economist, ed. "Cité Nouvelle". Visit Sept. 1942'] and the inclusion of a business card for Monseigneur Henri Petit, Prélat de sa Sainteté, Vicaire Général, Geneva, with a handwritten note in French on it.

Handwritten and typed diary entries relating to Lester's time as Acting Secretary General of the League of Nations in Geneva. Includes numerous diary entries and correspondence concerning Lester's threat to resign his position in June 1941 following his discovery that his name was apparently on a British secret service 'watch list'. Diary includes correspondence with Seán T Ó Ceallaigh [Sean T O'Kelly], Minister for Finance; James John McElligott, Secretary of the Department of Finance; James Dillon, TD (letter from Lester was unsent); Seymour Jacklin, Treasurer of the League of Nations; Carl Hambro, Head of the Supervisory Commission of the League of Nations; Hugh McKinnon Wood, Counsellor and Legal Adviser at the League of Nations; Arthur Sweetser, League of Nations' Public Information Section; Frank P Walters, Deputy Secretary General of the League of Nations; Roger Makins, British Foreign Office; Anthony Eden, British Secretary of State for Foreign Affairs; Alexander Cadogan, British Permanent Under-Secretary for Foreign Affairs; David V Kelly, British Legation in Berne, Switzerland; Harry Livingston, British Consulate in Geneva; Lord Davies [David Davies, 1st Baron Davies]; Robert Cecil, 1st Viscount Cecil of Chelwood; Robert Collis, doctor and author; Frank T Cremins, Irish Legation in Berne, Switzerland; Ernst Grunwald ('[an] Austrian textile trader, who was in a civilian camp in Switzerland with his wife and obtained visas thanks to S. Lester's help', according to the finding aid for the Sean Lester collection in the United Nations Archives, Geneva. See reference: PP 274/2/871-873); Gretta Lester, Seán Lester's sister, and Frank Lidgett McDougall, Australia House, London. Also includes several Christmas cards and business cards from various diplomats, dignitaries and friends.

Handwritten and typed diary entries relating to Lester's time as Acting Secretary General of the League of Nations in Geneva. One of the most notable entries in this diary is Lester's extensive account of his meeting with James Joyce and his family in Geneva in December 1940. The Joyce family had fled their home in Paris the previous May and sought Lester's help in obtaining a visa for their daughter Lucia; the Nazis had refused to issue her with a visa and she remained in a mental health clinic in German-occupied France. A related letter from Joyce to Lester prior to this meeting is also included in the diaries, as are letters from Giorgio Joyce, son of James and Nora Barnacle [Joyce], and Carola Giedion-Welcker, a German-Swiss art historian and close friend of the Joyce family, following the death of James Joyce in Zurich less than a month later. Diary also includes letters and telegrams from: Alec [Alexander] Loveday, Director of the Economic, Financial, and Transit Department of the League; Sir Walford Selby, British diplomat; Arthur Sweetser, League of Nations Public Information Section; John Gilbert Winant, Director- General of International Labour Organisation; [Humphrey] Hume Wrong, Canadian Advisory Officer to the League of Nations; Elizabeth Wiskemann, British historian; Royall Tyler, Economic and Financial Section of the League of Nations; Carl Hambro, Head of the Supervisory Commission of the League, and René Massigli, French diplomat. Also includes letters and telegrams to: Ned [Edward Joseph] Phelan, International Labour Organisation; Carl Hambro, Head of the Supervisory Commission of the League; Elsie Lester; copy letter from Seán Murphy, Irish Minister Plenipotentiary in France to James Joyce, author; Nora Barnacle, wife of James Joyce, and Frank P Walters, Deputy Secretary General of the League of Nations. Some of the diary entries and correspondence 15 feature codenames with later annotations by Lester giving the individuals' real names. Diary also includes two black and white photographs: one of the overturned bus that Alec [Alexander] Loveday and others had been travelling in when it crashed near Grenoble, France, in August 1940, and the other is of a Connemara pony taken by Ann Lester [Gorski].

Consists of handwritten and typed diary entries, letters, postcards and other documents. Topics include Lester's final months as Deputy Secretary General of the League of Nations; his assuming the role of Acting Secretary General following the resignation of Joseph Avenol on 31 August 1940; the dire state of the Secretariat finances, and a bus crash in August involving several League of Nations employees, including Alec [Alexander] Loveday, while travelling to Lisbon, Portugal, as part of the transfer of the Secretariat's technical services to Princeton, USA [a photograph of the crashed bus is included in diary C1/9]. Diary includes letters to Lester from: Alec Loveday, Director of the Economic, Financial, and Transit Department of the League of Nations; Seymour Jacklin, Treasurer of the League of Nations; Carl Hambro, Head of the Supervisory Commission of the League of Nations; Thamassis Aghnides, Director of the Disarmament Section of the League of Nations; Arthur Sweetser, League of Nations' Public Information Section; Hugh McKinnon Wood, Counsellor and Legal Adviser at the League of Nations; Laurence C Tombs, a former official in the Transit and Communications Section of the League of Nations; Edward Joseph Phelan, International Labour Organisation, and Carl Jacob Burckhardt, International Committee of the Red Cross [and previously, Lester's successor as League of Nations High Commissioner in Danzig]. Also includes newspaper cuttings and black and white passport photograph of an unidentified man.

Handwritten and typed diary entries relating to Lester's time as Deputy Secretary General of the League of 12 Nations in Geneva, the outbreak of the Second World War, and the evacuation of his wife and three daughters from Geneva to Ireland. Includes letters and cards to Lester from: Jack T Mayo ['an English fishing companion']; Ambrose B Wareing, the Danzig correspondent for the Daily Telegraph newspaper (letter dated 16 June 1937); Isidro Fabela, Mexican diplomat; Pierre Stoppani, League of Nations Economic Relations Section; Eóin MacNeill, Professor, National University of Ireland; Vladimir Sokoline, Under Secretary General's Office, League of Nations; Stephen Gwynn, former MP for Galway city, academic and journalist; S Pelychuoniades, Hellenic Delegation to the League of Nations; Joseph MN Jeffries, author and journalist; Phyllis Manning, a friend who it seems, also holidayed in Connemara and who worked at the Agricultural Economics Research Institute in Oxford, and GC Greene, 'British Sporting Agency Ltd, Digswell Vale, Welwyn, Hertfordshire, UK. Includes extract from letter written by Raymond Fosdick, Rockefeller Foundation, to Arthur Sweetser, League of Nations' Public Information Section. Also includes a handwritten 'note for talk with S.G.' [?Secretary General, Joseph Avenol], dated September 1938, newspaper cuttings, poems by Patricia E Lester [Seán Lester's daughter], and black and white photographs. First photograph features the following individuals chatting beside a bench in a garden or park 'at luncheon to [?Iroguiera' Luis Podestá Costa, League of Nations Under Secretary General; Frank P Walters, League of Nations Under Secretaries-Generals in charge of Political Section Office; Lester, and Isidro Fabela, Mexican diplomat. Second photograph features Lester, Alberto Guani, Uruguayan Foreign Minister, and [?Iroguiera] in Lester's office. There are two gaps in the diary when Lester did not record entries for months at a time. This diary opens with '[n]ot a line written in a notebook for months', and an entry on 31 January 1940 notes that '[n]othing written for 2 months'.

Handwritten and typed diary entries relating to Lester' time as Deputy Secretary General of the League of Nations in Geneva. Includes copy letters from Lester to: Joseph Avenol, Secretary General of the League of Nations, and RM Smyllie, editor of the Irish Times. Includes letters to Lester from: Daniel Anthony Binchy, University College Dublin lecturer and former Irish diplomat; John Marcus O' Sullivan, TD, academic and former member of the Irish delegation to the League of Nations; Alfred O’Rahilly, professor of mathematical physics at University College Cork, mainly concerning the potential promotion of O’Rahilly's new book Electromagnetics: A Discussion of Fundamentals in Switzerland; James Cousins, Irish writer and lecturer at the University of Travancore, India. Includes copy letters from: Arthur Sweetser to [?Lewis Lerwin] in the USA;, and HR Cummings, London representative of the League of Nations Secretary General, to Joseph Avenol. Also includes a list of names and occupations of individuals in the museum sector who attended at luncheon on 8 March [?1939].

Handwritten and typed diary entries relating to Lester's time as Deputy Secretary General of the League of Nations in Geneva. Includes draft letter from Lester to Anthony Eden, British Secretary of State for Foreign Affairs, and copy letter to HR Cummings, London representative of the Secretary General of the League of Nations.

Handwritten and typed diary entries relating to Lester's time as Deputy Secretary General of the League of Nations in Geneva. Includes newspaper cuttings and a programme for a St Andrew's Day dinner, hosted by the Caledonian Society of Switzerland on 4 December 1937 (at which Lester was a speaker).

Consists of unbound typed diary entries, documents and letters relating to Lester's final months as High Commissioner of the League of Nations in Danzig. Lester left Danzig on 22 December 1936 having been promoted to the position of Deputy Secretary General of the League. He took up his new appointment in Geneva on 16 January 1937. Includes document written by Lester outlining the context for the file: 'The following fragments are the only notes I have of my last six months in Danzig ... The reason they are so fragmentary ... was that the crisis in Danzig developed so quickly and in such uncertainty that I could not safely keep any record of certain matters, either in my house or my Office. For three months at any rate I was not at all sure that my house and Office might not be occupied any day by the political Police or the Storm Troopers [sic].' - Document comprising of two diary entries, the first from 6 May 1936 (pages 1-3) and the second from early July 1936 (pages 4-9) combined together as a single entry. The section from 6 May 1936 is duplicated in Diary 2: January-June 1936 in the collection [diary C1/2]. Includes diary entries (some marked 'Private Diary') from the following dates: 8, 17, [?20], 23 (two entries with this date, one titled 'Relations with Greiser'), 24, and 28 July 1936; 3, 5, 6 and 7 August 1936 (two copies); 12 September 1936; 16, 19 and 24 October 1936; 22 December 1936 and 1 February 1937. Entries were all written in Danzig apart from the final entry (1 February 1937) which was written in Geneva. Includes undated notes on Albert Forster, the Nazi Party's Gauleiter in Danzig, that was originally filed between diary entries from 24 October 1936 and 22 December 1936, and was thus possibly written during that period. Includes copy letters from Lester to Joseph Avenol, Secretary General of the League of Nations, from the following dates: 11, 14 and 24 July 1926; 1 August 1936 (two copies of two different letters from this date). Most of the letters are marked 'Personal', 'Personal and Confidential', or 'Personal; Secret'.

Handwritten and typed diary entries relating to Lester's time as High Commissioner of the League of Nations in Danzig. Includes telegram from Bishop Edward O'Rourke, Catholic Bishop of Danzig, to Lester dated 17 March 1936 with best wishes for St Patrick's Day, and letter from the Danzig Police President dated 21 March 1936, inviting Lester to the opening of the Danzig Trophy Show.

Consists of handwritten and typed diary entries relating to Lester's time as High Commissioner of the League of Nations in Danzig.