Rheiderland

thumb|The medieval region of Rheiderland (in red) which straddles the border in northwest Germany and northeast Netherlands.

The Rheiderland (; ) is a region of Germany and the Netherlands between the River Ems and the Bay of Dollart. The German part of the Rheiderland lies in East Frisia, west of the Ems. The Dutch part (written: Reiderland) lies in the Dutch province of Groningen and is mostly part of Oldambt. The Rheiderland is one of the four historic regions on the mainland in the district of Leer; the others being the Overledingerland, the Moormerland and the Lengenerland.