(Oct. 1–Nov. 15, 1818), the first of the four congresses held by Great Britain, Austria, Prussia, Russia, and France to discuss and take common action on European problems following the Napoleonic Wars (1800–15). This congress (held at Aix-la-Chapelle—now Aachen, Ger.) was attended by Alexander I of Russia, Francis I of Austria, Frederick William III of Prussia, and their representatives. Great Britain was represented by Viscount Castlereagh and by the duke of Wellington. Armand-Emmanuel, duke de Richelieu (Richelieu, Armand-Emmanuel du Plessis, duke de), represented France. The later congresses were held at Troppau (Troppau, Congress of) (1820), Laibach (Laibach, Congress of) (1821), and Verona (Verona, Congress of) (1822).

At the first session Richelieu offered to pay most of the war indemnity owed by France to the allies in return for the withdrawal of their armies of occupation by November 30. This offer was accepted. On October 9 a treaty was signed settling the claims against France as a result of the wars. France was admitted to the new Quintuple Alliance as an equal. Although the old Quadruple Alliance (Quadruple Alliance) of Great Britain, Austria, Prussia, and Russia was secretly renewed in a protocol signed on November 15, this renewal was largely a formality.

The congress also discussed suppression of the slave trade and of the Barbary pirates, but no decision was reached. The status of Jews and many other questions were considered.