The Locarno Treaties were seven agreements negotiated at Locarno, Switzerland, on 5 October – 16 October 1925 and formally signed in London on 3 December, in which the First World War Western European Allied powers and the new states of central and Eastern Europe sought to secure the post-war territorial settlement, and return normalizing relations with defeated Germany (which was, by this time, the Weimar Republic). Ratifications for the Locarno treaties were exchanged in Geneva on 14 September 1926, and on the same day they became effective. The treaties were also registered in the League of Nations Treaty Series on the same day.

Locarno divided borders in Europe into two categories: western, which were guaranteed by Locarno treaties, and eastern borders of Germany with Poland, which were open for revision, thus leading to German renewed claims to the Free City of Danzig and Polish territories approved by the League of Nations including the Polish Corridor, and Upper Silesia.

The Locarno discussion arose from exchanges of notes between the British Empire, France and Germany over the summer of 1925 following German foreign minister Gustav Stresemann's 9 February proposal for a reciprocal of his country's western frontiers as established under the unfavourable 1919 Treaty of Versailles, as a means of facilitating Germany's diplomatic rehabilitation among the Western Powers.