Kwidzyn (; ; Prussian: Kwēdina) is a town in northern Poland on the Liwa river, with 40,008 inhabitants (2004). It has been a part of the Pomeranian Voivodeship since 1999, and was previously in the Elbląg Voivodeship (1975–1998). It is the capital of Kwidzyn County.
The Teutonic Knights founded an Ordensburg castle in 1232 and a town the following year. In 1243 the Bishopric of Pomesania received both the town and the castle of Marienwerder (German for "Mary's ait") from the Teutonic Order as fiefs, and the settlement became the seat of the Bishops of Pomesania within Prussia. The town was populated with Masurian settlers. Werner von Orseln, who died in Marienburg (Malbork) in 1330, was buried in the cathedral of the town. St. Dorothea of Montau lived here from 1391 until her death in 1394; pilgrims would later come to pray in the town at her shrine. The rebellious Prussian Confederation was founded in the town on March 14, 1440. In 1466, the town became a Polish fief together with the remainder of the monastic state of the Teutonic Knights after their defeat in the Thirteen Years' War.
It became part of the Duchy of Prussia, a fief of Poland, upon its creation in 1525. The duchy was inherited by the House of Hohenzollern in 1618 and was elevated to the Kingdom of Prussia in 1701. The town became the capital of the District of Marienwerder. When after the First Partition of Poland, resulting in the re-unification of Prussia, the new Prussian Province of West Prussia was founded, Marienwerder was taken out of the Province of East Prussia and integrated into West Prussia of which it became the administrative seat. The town and district were included within the government region of Marienwerder after the Napoleonic Wars.
In 1885 the town had 8,079 mostly Lutheran inhabitants, many of whose trades were connected with the manufacturing of sugar, vinegar, and machines. Other trades were brewing, dairy farming, and fruit-growing. According to official statistics, c. 1910, 35.7% of the county's population was Polish.
After World War I most of West Prussia was incorporated into the Polish Second Republic. The treaty of Versailles permitted the plebiscite East Prussia, to determine if the town would remain in Germany as part of East Prussia or join Poland; 93,73% of the inhabitants of the town voted on 11 July 1920 for East Prussia, to which the town was joined.
On November 10, 1937, when the Nazi regime was already in power in Germany, a Polish private high school was opened in Marienwerder, which was closed down by force on August 25, 1939.
On 30 January 1945 during World War II, the town was captured by the Soviet Red Army. Red Army established a war hospital in the town for 20,000 people. The town's old center was burned by Soviet soldiers. The town became part of Poland in 1945, after World War II as a result of the Potsdam Conference. Burned parts of the town's old center were dismantled to provide material for the rebuilding of Warsaw after its destruction in the Warsaw Uprising.