三帝同盟（德语：Dreikaiserabkommen，俄语：Союз трёх императоров），感到法国想报普法战争（1870年－1871年）之仇、取回阿尔萨斯-洛林（割让给德国的领土），德国首相俾斯麦欲恢复由俄皇亚历山大一世发起的神圣同盟，以及防止俄国与法国联手，发动战争东西夹击德国，于是撮合俄罗斯沙皇亚历山大二世，德国皇帝威廉一世及奥匈帝国皇帝法兰西斯·约瑟夫于1873年签署以孤立法国为目标的三帝同盟。

The League of the Three Emperors was an alliance between the German Empire, the Russian Empire and Austria-Hungary, from 1873 to 1887. Chancellor Otto von Bismarck took full charge of German foreign policy from 1870 to his dismissal in 1890. His goal was a peaceful Europe, based on the balance of power. Bismarck feared that a hostile combination of Austria, France and Russia would crush Germany. If two of them were allied, then the third would ally with Germany only if Germany conceded excessive demands. The solution was to ally with two of the three. In 1873 he formed the League of the Three Emperors, an alliance of the Kaiser of Germany, the Tsar of Russia, and the Kaiser of Austria-Hungary. Together they would control Eastern Europe, making sure that restive ethnic groups such as the Poles were kept in control. It aimed at neutralizing the rivalry between Germany’s two neighbors by an agreement over their respective spheres of influence in the Balkans and at isolating Germany’s enemy, France. The Balkans posed a more serious issue, and Bismarck's solution was to give Austria predominance in the western areas, and Russia in the eastern areas.