The Bourtanger Moor (Dutch: Bourtangerveen/Bourtangermoeras) (German: Bourtanger Moor) was a bog in eastern parts in the Dutch provinces of Drenthe and Groningen and the bordering German districts of Bentheim and Emsland. A remaining stretch on the border between Drenthe and the districts Emsland and Betheim is now a nature reserve, the Internationaler Naturpark Bourtanger Moor-Bargerveen.
The Bourtange Swamp had the shape of a V. The western leg covered the valley of the Hunze and ranged towards the city of Groningen. The western part was bordered by the Hondsrug. The eastern leg was located in the valley of the Ems. Between these two legs lays Westerwolde. At its greatest extent the swamp was about 3000 km².
The swamp arose around 5000 BC. The area was already inhabited before this happened, as shown by archeological finds such as the one at Hoetsmansmeer in Groningen. These finds are attributed to nomads from the Mesolithic. Eventually these people left because of the growing swamp. Near Valthe - Ter Apel and Nieuw-Dordrecht renmants of roads through the bog were found, dating from the Neolithic to the Iron age.
From a military point of view the swamp had an important function as a protective barrier, especially between 1580 and 1850. The swamp played an important role during the wars between Groningen and Münster In places with passages through or along the bog, strongholds were built. Bourtange, Oudeschans, Nieuweschans, Valtherschans and Emmerschans are examples of these places.