Frisia (or more commonly "Friesland") is a region along the southeastern coasts of the North Sea. Frisia extends from the northeastern Netherlands to southwestern Denmark. Western Frisia is roughly identical with the Dutch province of Friesland, the northern portion of North Holland Province and also modern Groningen Province, though the Western Frisian language is only spoken in the first.

Eastern Frisia (German Ostfriesland) includes areas located in the northwest of the German state of Lower Saxony, including the districts of Aurich, Leer, Wittmund and Friesland, as well as the district-free towns of Emden and Wilhelmshaven.

The portions of Frisia within the state of Schleswig-Holstein are called Nordfriesland and stretch along the coast, and including also the coastal islands islands from the River Eider to the border of Denmark in the north. It is coterminous with the Schleswig-Holstein district of the same name. The island of Helgoland (Eng. 'Helligoland' and Nrth. Fries. 'Lun', is also part of traditional 'Northern Frisia').

The West Frisian Islands, the East Frisian Islands and previously noted North Frisian Islands stretch along the entirety of the Frisian coast.

A half million Frisians of Friesland or Fryslan province in the Netherlands speak the Frisian language. Several thousand more Frisian language speakers, speaking a collection of dialects often unintelligible with each other and certainly unintelligible with forms spoken beyond Nordfriesland, are to be found in Nordfriesland in Germany, while a small number of speakers of the Sater-Frisian language are located in four villages of Lower Saxony in the Saterland region of Cloppenburg county, just beyond the boundaries of traditional East Frisia.