Overijse is a municipality in the province of Flemish Brabant, in Flanders, one of the three regions of Belgium. The municipality comprises the town of Overijse, and the communities of Eizer, Maleizen, Jezus-Eik, Tombeek and Terlanen. On December 31, 2008 Overijse had a total population of 24,410. The total area is 44.43 km² which gives a population density of 549 inhabitants per km². Overijse is surrounded by an extensive woodlands (Zoniënwoud/Forêt de Soignes), with walk- and bicycle paths. The community is regarded as a very attractive area in which to live.
The official language is Dutch. French-speaking residents who have migrated mainly from Wallonia or Brussels are represented by 8 members on the 27-seat local council. According to the 2008 census, Overijse was also home to 4,842 expatriates including 1,236 Dutch, 766 British, 505 Germans, 375 Americans, 311 French and 295 Italian.
Near Overijse there is a medium wave transmitter for the Belgian foreign radio service. Overijse has a traditional festival every year, held in August (Druivenfeesten). The festival commemorates the industry that shaped the area, namely cultivation of grapes (Dutch druiven). In 2010 it is held from August 21–28. The Druivenkoers Overijse is a single-day road bicycle race during the festival. The Vlaamse Druivencross is a December cyclo-cross classic race.
In 1952, Albert Lootvoet, a local brewer started brewing the now world-famous Leffe beer according to its original recipe. The Leffe beers were brewed in Overijse from 1952 until 1977, when the Artois breweries bought out the local brewer.