The Treaty of Athis-sur-Orge was a peace treaty signed on 23 June 1305 between King Philip IV of France and Robert III of Flanders. The treaty was signed at Athis-sur-Orge after the Battle of Mons-en-Pvle and concluded the Franco-Flemish War (1297-1305).

Despite winning the battle at Mons-en-Pvle, Philip's kingdom was too financially and militarily drained to take advantage of it. The treaty instead imposed a heavy price.

Flanders (UK: , US: ; Dutch: Vlaanderen [ˈvlaːndərə(n)] (listen); French: Flandre [flɑ̃dʁ]; German: Flandern [ˈflandɐn]) is the Dutch-speaking northern portion of Belgium and one of the communities, regions and language areas of Belgium. However, there are several overlapping definitions, including ones related to culture, language, politics, and history, and sometimes involving neighbouring countries. The demonym associated with Flanders is Fleming, while the corresponding adjective is Flemish. The official capital of Flanders is the City of Brussels, although the Brussels-Capital Region has an independent regional government. The government of Flanders only oversees the community aspects of Flanders life in Brussels, such as Flemish culture and education.

Flanders, despite not being the biggest part of Belgium by area, is the area with the largest population (68.2%) if Brussels is included. 7,798,652 out of 11,431,406 Belgian inhabitants live in Flanders or the bilingual Brussels region. Only about 8% of Brussels inhabitants identify as Flemish, while the rest identify as French-speaking. Not including Brussels, there are five present-day Flemish provinces.

In medieval contexts, the original "County of Flanders" stretched around AD 900 from the Strait of Dover to the Scheldt estuary and expanded from there. This county also still corresponds roughly with the modern-day Belgian provinces of West Flanders and East Flanders, along with neighbouring parts of France and the Netherlands. Although this original meaning is still relevant, in modern times the term "Flanders" came to refer to a larger area, and is used to refer to the entire Dutch-speaking part of Belgium, stretching all the way to the Meuse, as well as cultural movements such as Flemish art. In accordance with late 20th century Belgian state reforms the Belgian part of this area was made into two political entities: the "Flemish Community" (Dutch: Vlaamse Gemeenschap) and the "Flemish Region" (Dutch: Vlaams Gewest). These entities were merged, although geographically the Flemish Community, which has a broader cultural mandate, covers Brussels, whereas the Flemish Region does not.

The area of today's Flanders, by every definition, has figured prominently in European history since the Middle Ages. In this period, cities such as Ghent and Bruges of the historic County of Flanders, and later Antwerp of the Duchy of Brabant made it one of the richest and most urbanised parts of Europe, trading, and weaving the wool of neighbouring lands into cloth for both domestic use and export. As a consequence, a very sophisticated culture developed, with impressive achievements in the arts and architecture, rivaling those of northern Italy. Belgium was one of the centres of the 19th-century industrial revolution, but Flanders was at first overtaken by French-speaking Wallonia. In the second half of the 20th century, and due to massive national investments in port infrastructure, Flanders' economy modernised rapidly, and today Flanders and Brussels are much wealthier than Wallonia. They are among the wealthiest regions in Europe and the world.Geographically, Flanders is mainly flat, and has a small section of coast on the North Sea. Much of Flanders is agriculturally fertile and densely populated, with a density of 483/km2 (1,250/sq mi). It touches the French department of Nord to the southwest near the coast, and borders the Dutch provinces of Zeeland, North Brabant and Limburg to the north and east, and the Walloon provinces of Hainaut, Walloon Brabant and Liège to the south. The Brussels Capital Region is an officially bilingual enclave within the Flemish Region. Flanders has exclaves of its own: Voeren in the east is between Wallonia and the Netherlands and Baarle-Hertog in the north consists of 22 exclaves surrounded by the Netherlands.