Westphalian or Westfalish (Standard High German: Westfälisch [vɛstˈfɛːlɪʃ] ^ⓘ, Standard Dutch: Westfaals [ʋɛstˈfaːls] ^ⓘ) is one of the major dialect groups of Low German. Its most salient feature is its diphthongization (rising diphthongs). For example, speakers say iäten ([ɪɛtn̩]) instead of etten or äten for "to eat". (There is also a difference in the use of consonants within the Westphalian dialects: North of the Wiehengebirge, people tend to use unvoiced consonants, whereas south of the Wiehengebirge they tend to use the voiced equivalents, e.g. Foite > Foide.)

The Westphalian dialect region includes the north-eastern part of North Rhine-Westphalia, i.e. the former Prussian province of Westphalia, without Siegerland and Wittgenstein, but including the southern part of former government district Weser-Ems (e.g. the region around Osnabrück and the landscape of Emsland in modern Lower Saxony).

Traditionally, all Dutch Low Saxon dialects are considered Westphalian, with the notable exception of Gronings, which is grouped with the Northern Low Saxon and Friso-Saxon dialects.^{[citation needed]} The rising diphthongisation is still noticeable in the dialects of Rijssen, Enter and Vriezenveen. In a band from southeast Twente to northwest Twente the diphtongisation still happens before the consonants v, g and z. Vriezenveen furthermore preserved the diphtongisations in words like to eat, to hope and kitchen. In other areas of Dutch Low Saxon the breaking was monophthongized and then highered and lengthened, resulting in different development stadia away from the breaking depending on the area.

Among the Westphalian language there are different subgroups of dialects:

Westphalian dialects in Westphalia

Westphalian dialects in the Netherlands:

Westphalian dialects in Lower Saxony and Groningen

Westphalian has many lexical similarities and other proximities to Eastphalian, extending to the East and slightly to the North of the area where Westphalian is spoken.