report of an encounter between King William I of Prussia and the French ambassador; the telegram was sent from Ems (Bad Ems) in the Prussian Rhineland on July 13, 1870, to the Prussian chancellor, Otto von Bismarck (Bismarck, Otto von). Its publication in a version edited by Bismarck so as to purposely offend the French government precipitated the Franco-German War.

Early in July, the candidacy of Prince Leopold of Hohenzollern-Sigmaringen, a relative of the Prussian king, for the Spanish throne had alarmed the French, who feared that the extension of Prussian influence into Spain would threaten France. Leopold's candidacy was withdrawn on July 12; the following day, the French ambassador to Prussia, Count Vincent Benedetti (Benedetti, Vincent, Comte), approached King William (William I) at Ems to request an assurance that no member of his family would again be a candidate for the Spanish throne. The king politely refused Benedetti's demand, and their discussion ended.

A telegram describing the incident was sent to Bismarck. Bismarck's edited version, which he published the next day, omitted the courtesies in the two men's exchange and instead made it seem that each man had insulted the other. This touched off an intensified demand for war in Paris and Berlin, and France declared war on July 19. The incident provided the excuse for a trial of strength that was sought by both France and Prussia, but because of Bismarck's dishonest editing of the Ems telegram, it was France that was the first to declare war. This circumstance helped enlist the southern German states to Prussia's side in the ensuing war, which resulted in the unification of all the German states (except Austria) into modern Germany.