Triple Alliance, a name given to several international agreements. The most important was a secret treaty that was signed by Germany, Austria-Hungary, and Italy in 1882 and remained in effect until 1915. It resulted in a division of European powers into two opposing blocs and thus contributed to the outbreak of World War I.

The alliance developed from a mutual-defense pact made by Germany and Austria-Hungary in 1879, mainly as a protection against Russia. France was also regarded as a potential enemy by Germany. When the French occupied Tunisia in 1881, forestalling its seizure by the Italians, Italy joined the other two countries to form the Triple Alliance. The alliance was counterbalanced by the Triple Entente. In 1914 Austria-Hungary, assured of German support on the basis of the Triple Alliance, attacked Serbia and precipitated World War I. Italy refused to honor the alliance and fought on the other side.

Other notable treaties by this name were:

Triple Alliance of 1668,

between England, Holland, and Sweden, for protection against French territorial ambitions.

Triple Alliance of 1717,

between Great Britain, Holland, and France, to force Spain to abide by the provisions of the Peace of Utrecht. When Austria joined in 1718, this alliance became known as the Quadruple Alliance.