The Achterhoek (Dutch pronunciation: [ˈax.tər.ˌɦuk]) is a region in the eastern part of the Netherlands, Europe.

Its name (meaning "rear-corner") is geographically appropriate because the area lies in the Eastern-most part of Gelderland, and therefore of the Netherlands, protruding into Germany. The Achterhoek area lies between the rivers IJssel and Oude IJssel, and the borders with the province of Overijssel and Germany the former region of Zutphen County. The region is predominantly rural, with lots of free space, forests and farms. The area around the town of Winterswijk is regarded as very beautiful. A well-known beer originates from this region: Grolsch beer was first brewed in Groenlo in 1615.

The original language of the Achterhoek is Achterhooks, a variety of Low Saxon. The language can also differ per municipality/town, even in such a way that a person speaking the 'Grols' variant will probably not be understood by a person from Winterswijk which is merely 10km to the east. The number of inhabitants whose sole language is Achterhooks has greatly declined over the last 60 years, inhabitants are raised with the Dutch at school and the dialect is only spoken (sometimes) at home. Partly due to immigration from outside the Achterhoek region and the effects of national government, the Dutch language is having a significant impact on the dialect. Many old words have been forgotten and replaced by their Dutch-derived equivalents.