West Frisian, or simply Frisian or Frysk, is a West Germanic language spoken mostly in the province of Friesland (Fryslân) in the north of the Netherlands. It is the most widely spoken of the Frisian languages.

Fryslân has ca. 650,000 inhabitants of whom 94% can understand spoken West Frisian, 74% can speak West Frisian, 75% can read West Frisian, and 27% can write it.

For over half of the inhabitants of the province of Fryslân, West Frisian is the native language. In the central east, West Frisian speakers spill over the province border, with some 4,000–6,000 of them actually living in the province of Groningen. Also, many West Frisians have left their province in the last 60 years for more prosperous parts of the Netherlands. Therefore, possibly as many as 150,000 West Frisian speakers live in other Dutch provinces. Apart from the use of West Frisian as a first language, it is also spoken as a second language by about 120,000 people in the province of Fryslân.

West Frisian is considered by UNESCO to be a language in danger of becoming extinct, officially being listed as "Vulnerable".

West Frisian is standardised and that standard is widely accepted by Frisian society. West Frisian is officially recognised by the Dutch Government and has had official status in the province of Fryslân since 1956. In 2014 the Dutch Government passed the Frisian Language Act which guarantees the right of everyone in the Province of Fryslân to use their own language in court and with administrative bodies and which makes Dutch and Frisian the two official languages of the province of Fryslân.

Primary education in Friesland was made bilingual in 1956, which means West Frisian can be used as a teaching medium. In the same year, West Frisian became an official school subject, having been introduced to primary education as an optional extra in 1937. It was not until 1980, however, that West Frisian had the status of a required subject in primary schools, and not until 1993 that it was given the same position in secondary education.

Within ISO 639 West Frisian falls under the codes fy and fry, which were assigned to the collective Frisian languages.