Deventer (Dutch: [ˈdeːvəntər] (listen); Sallands: Daeventer) is a city and municipality in the Salland historical region of the province of Overijssel, Netherlands. In 2020, Deventer had a population of 100,913. The city is largely situated on the east bank of the river IJssel, but it also has a small part of its territory on the west bank. In 2005 the municipality of Bathmen (with a population of about 5,000 people) was merged with Deventer as part of a national effort to reduce bureaucracy in the country.

Deventer is one of the oldest cities in the Netherlands. The place is mentioned in 9th-century sources from the Diocese of Utrecht. A charter from 877 AD mentions seven hooves in Daventre portu (the Deventer harbor). In 952 AD, Deventer is mentioned as a city in a gift certificate from King Otto I. After the place had acquired more and more rights and privileges over time, it received the municipal lands from Emperor Henry V in 1123. This is considered by historians to be the moment of Deventer obtaining the city rights by the inhabitants. The city has the oldest stone house, the oldest walking park and with the Athenaeum library also the oldest scientific library in the Netherlands.