Borkum is an island and a municipality in the Leer District in Lower Saxony, northwestern Germany.
Borkum is bordered to the west by the Westerems strait (which forms the border with the Netherlands), to the east by the Osterems strait, to the north by the North Sea, and to the south by the Wadden Sea. It is the largest and westernmost of the East Frisian Islands in the North Sea, due north of the Dutch province of Groningen.
The island was formed by two previously separate islands which were still separated by a shallow water in 1863. The seam between the former eastern and western parts is called Tüskendör ("through in between").