The Congress of Vienna of 1814–1815 was a series of international diplomatic meetings to discuss and agree upon a possible new layout of the European political and constitutional order after the downfall of the French Emperor Napoleon Bonaparte. Participants were representatives of all European powers (other than the Ottoman Empire) and other stakeholders. The Congress was chaired by Austrian statesman Klemens von Metternich, and was held in Vienna from September 1814 to June 1815.

The objective of the Congress was to provide a long-term peace plan for Europe by settling critical issues arising from the French Revolutionary Wars and the Napoleonic Wars through negotiation. The goal was not simply to restore old boundaries, but to resize the main powers so they could balance each other and remain at peace, being at the same time shepherds for the smaller powers. More generally, conservative leaders like Metternich also sought to restrain or eliminate republican, liberal, and revolutionary movements which, from their point of view, had upended the constitutional order of the European ancien régime.

At the negotiation table, the position of France was weak in relation to that of Britain, Prussia, Austria, and Russia, partly due to the military strategy of its leader, Napoleon Bonaparte, over the previous two decades, and his recent defeat. In the settlement the parties did reach, France had to give up all recent conquests, while the other three main powers made major territorial gains around the world. Prussia added territory from smaller states: Swedish Pomerania, most of the Kingdom of Saxony, and the western part of the former Duchy of Warsaw. Austria gained much of northern Italy. Russia added the central and eastern parts of the Duchy of Warsaw. All agreed upon ratifying the creation of the new Kingdom of the Netherlands, which had been created just months before from the former Dutch Seven Provinces together with formerly Austrian territory, and was meant to serve as a buffer between the German Confederation and France.

The immediate background was Napoleonic France's defeat and surrender in May 1814, which brought an end to 23 years of nearly continuous war. Remarkably, negotiations continued unaffected despite the outbreak of fighting triggered by Napoleon's return from exile and resumption of power in France during the Hundred Days of March to July 1815. The Congress's agreement was signed nine days before Napoleon's final defeat at Waterloo on 18 June 1815.

Some historians have criticised the outcomes of the Congress for causing the subsequent suppression of national, democratic, and liberal movements, and it has been seen as a reactionary settlement for the benefit of traditional monarchs. Others have praised the Congress for protecting Europe from large and widespread wars for almost a century.

The name "Congress of Vienna" was not meant to suggest a formal plenary session, but rather the creation of a diplomatic organizational framework bringing together stakeholders of all flocks to enable the expression of opinions, interests and sentiments and facilitate discussion of general issues among them. The Congress format had been developed by Austrian Foreign Minister Klemens von Metternich, assisted by Friedrich von Gentz, and was the first occasion in history where, on a continental scale, national representatives and other stakeholders came together in one city at the same time to discuss and formulate the conditions and provisions of treaties. Before the Congress of Vienna the common method of diplomacy involved the exchange of notes sent back and forth among the several capitals and separate talks in different places, a cumbersome process that required much in the way of time and transportation. The format set at the Congress of Vienna would serve as inspiration for the 1856 peace conference brokered by France (the Congress of Paris) that settled the Crimean War. The Congress of Vienna settlement gave birth to the Concert of Europe, an international political doctrine that emphasized the maintaining of political boundaries, the balance of powers, and respecting spheres of influence and which guided foreign policy among the nations of Europe until the outbreak of the First World War in 1914.

To reach amiable consensus among the many different nations holding great interest in the settlement proceedings, informal, face-to-face deliberative sessions were held where opinions and proposed solutions could be inventoried. The policy work on which the Concert of Europe was built on came about through closed-doors dealing among the five Great Powers – Austria, Britain, Russia, Prussia and France. The first four of the five dominant peacemakers held sway simply because they brought to the table "negotiating power" that came of hard-won victory in the Napoleonic Wars; France enjoyed her advantageous position largely through the brilliant diplomatic maneuvering by senior statesman Talleyrand. Lesser powers, like Spain, Sweden, and Portugal, were given few opportunities to advocate their interests and only occasionally partook in the meetings held between the great powers. However, because all representatives were gathered in one city it was relatively easy to communicate, to hear and spread news and gossip, and to present points of view for both powerful and less powerful nations. Also of great importance to the parties convened in Vienna were the opportunities presented at wine and dinner functions to establish formal relationships with one another and build up diplomatic networks.

The Treaty of Chaumont in 1814 had reaffirmed decisions that had been made already and that would be ratified by the more important Congress of Vienna. They included the establishment of a confederated Germany, the division of Italy into independent states, the restoration of the Bourbon kings of Spain, and the enlargement of the Netherlands to include what in 1830 became modern Belgium. The Treaty of Chaumont became the cornerstone of the European Alliance that formed the balance of power for decades.