The Castle of the Teutonic Order in Malbork, commonly known as Malbork Castle (Polish: Zamek w Malborku; German: Ordensburg Marienburg), is a 13th-century castle complex located in the town of Malbork, Poland. It is the largest castle in the world measured by land area and a UNESCO World Heritage Site.

It was originally constructed by the Teutonic Order, a German Catholic religious order of crusaders, in the form of an Ordensburg fortress and named Marienburg in honour of Mary, mother of Jesus. In 1457, during the Thirteen Years' War, the castle was sold by Bohemian mercenaries to King Casimir IV of Poland in lieu of indemnities. It then served as one of several Polish royal residences and the seat of Polish offices and institutions, interrupted by several years of Swedish occupation, fulfilling this function until the First Partition of Poland in 1772. From then on, the castle was under German rule for over 170 years until 1945, albeit largely falling into disrepair as military technological advances rendered the castle a mere historical point of interest.

The construction period is a point of debate, but most historians generally accept the 132 years between 1274 and 1406 as the construction time. The castle is a classic example of a medieval fortress and, upon its completion in 1406, was the world's largest brick castle.

UNESCO designated the "Castle of the Teutonic Order in Malbork" and the Malbork Castle Museum a World Heritage Site in December 1997. It is one of two World Heritage Sites in the region (north-central Poland), together with the "Medieval Town of Toruń", which was founded in 1231. Malbork Castle is also one of Poland's official national Historic Monuments (Pomnik historii), as designated on 8 September 1994. Its listing is maintained by the National Heritage Board of Poland.