The West Germanic languages constitute the largest of the three branches of the Germanic family of languages (the others being the North Germanic and the extinct East Germanic languages). The West Germanic branch is classically subdivided into three branches: Ingvaeonic, which includes English, the Low German languages, and the Frisian languages; Istvaeonic, which encompasses Dutch and its close relatives; and Irminonic, which includes German and its close relatives and variants.

English is by far the most widely spoken West Germanic language, with over one billion speakers worldwide. Within Europe, the three most prevalent West Germanic languages are English, German, and Dutch. Frisian, spoken by about 450,000 people, constitutes a fourth distinct variety of West Germanic. The language family also includes Afrikaans, Yiddish, Low Saxon, Luxembourgish, Hunsrik, and Scots. Additionally, several creoles, patois, and pidgins are based on Dutch, English, or German.

The Germanic languages are traditionally divided into three groups: West, East and North Germanic. In some cases, their exact relation was difficult to determine from the sparse evidence of runic inscriptions, so that some individual varieties have been difficult to classify. This is especially true for the unattested Jute language; today, most scholars classify Jute as a West Germanic variety with several features of North Germanic.

Until the late 20th century, some scholars claimed that all Germanic languages remained mutually intelligible throughout the Migration Period, while others hold that speakers of West Germanic dialects like Old Frankish and speakers of Gothic were already unable to communicate fluently by around the 3rd century AD. As a result of the substantial progress in the study of Proto-West Germanic in the early 21st century, there is a growing consensus that East and West Germanic indeed would have been mutually unintelligible at that time, whereas West and North Germanic remained partially intelligible.

Dialects with the features assigned to the western group formed from Proto-Germanic in the late Jastorf culture (c. 1st century BC). The West Germanic group is characterized by a number of phonological, morphological and lexical innovations or archaisms not found in North and East Germanic. Examples of West Germanic phonological particularities are:^{[page needed]}

A relative chronology of about 20 sound changes from Proto-Northwest Germanic to Proto-West Germanic (some of them only regional) was published by Don Ringe in 2014.

A phonological archaism of West Germanic is the preservation of grammatischer Wechsel in most verbs, particularly in Old High German. This implies the same for West Germanic, whereas in East and North Germanic many of these alternations (in Gothic almost all of them) had been levelled out analogically by the time of the earliest texts.

A common morphological innovation of the West Germanic languages is the development of a gerund.