West-Friesland is a region in the north-western Netherlands, in the province North Holland. The region covers an area of about 800 km² and consists of the municipalities of Alkmaar, Andijk, Drechterland, Enkhuizen, Harenkarspel, Heerhugowaard, Hoorn, Langedijk, Medemblik, Niedorp, Noorder-Koggenland, Obdam, Opmeer, Schagen, Stede Broec, Venhuizen, Wervershoof, Wester-Koggenland and Wognum. Major cities include Hoorn and Alkmaar. The region comes out of a province from Westfriesland called Westflinge, wich is about same size modern West-Friesland.

The river Fli (or Flehi), an extension of the IJssel branch of the Rhine, divided the northern part of the Netherlands, which at the time all belonged to Friesland and was called Westfriesland, into a western and eastern part. In the 11th century, after heavy rainfalls, the river flooded and inundated large parts of the land; and not long after the Zuiderzee bay, previously a lake, was formed. In medieval times, West-Friesland practically was an island, bordered on the north by the Medem and Zijpe inlets, and to the south by various interconnecting lakes now laid dry that were in open connection with the Zuiderzee.

De region West-Friesland has from the 13th century been protected by the Westfriese Omringdijk ("West Frisian Ring Dike"), a dike that was built to protect the land against the salt water of the Zuiderzee. To this day the dike protects the eastern part of West-Friesland against the IJsselmeer and Markermeer.

For about 300 years, Westfriesland operated as an autonomous area as the Westfrisians did not want to be subjected to Hollandic authorities. Floris V, Count of Holland tried hard during his reign, but it was his successor John II who finally defeated the Westfrisians in 1297, putting an end to their independence. However, even though Westfriesland formed one united province with Holland in the Dutch Republic, it was recognized a separate region and the parliament of said province, commonly known as Holland, was formally known as the States of Holland and Westfriesland, showing that Westfriesland was still recognized in its own right.