The UPU held Congresses at the places & years listed below. A "Y" in the first column means that the APS Library has a printed copy of the Treaty agreed by the Congress in the version issued by the Austrian Government (which can be dated up to a year after the event). Some decisions are noted.
| | Berne 1874 (15 September to 9 October) |
| | Paris 1878 (2 May to 4 June) | Insured letters; Money Orders |
| | Lisbon 1885 (4 February to 21 March) |
| | Vienna 1891 (20 May to 4 July) | Subscriptions to newspapers and periodicals |
| | Washington 1897 (5 May to 15 June) |
| | Rome 1906 (7 April to 26 May) | International reply coupon |
| Y | Madrid 1920 (1 October to 30 November) | Giro transfers |
| Y | Stockholm 1924 (4 July to 28 August) |
| Y | London 1929 (10 May to 28 June) | Small packets |
| | Cairo 1934 (1 February to 20 March) |
| | Buenos Aires 1939 (1 April to 23 May) |
| | Paris 1947 (7 May to 5 July) | C.O.D. |
| | Brussels 1952 (14 May to 11 July) | Free post for POWS etc and the blind |
| | Ottawa 1957 (14 August to 3 October) |
| | Vienna 1964 (29 May to 11 July) |
| | Tokyo 1969 (1 October to 14 November) |
| | Lausanne 1974 (22 May to 4 July) |
| | Rio de Janeiro 1979 (12 September to 26 October) |
| | Hamburg 1984 (18 June to 27 July) |
| | Washington 1989 (13 November to 14 December) |
| | Seoul 1994 (22 August to 14 September) |
| | Beijing 1999 (23 August to 15 September) |
| | Bucharest 2004 (15 September to 5 October) |
| | Geneva 2008 (23 July to 12 August) |