Norwegian dialects (dialekter/ar) are commonly divided into four main groups, 'Northern Norwegian' (nordnorsk), 'Central Norwegian' (trøndersk), 'Western Norwegian' (vestlandsk), and 'Eastern Norwegian' (østnorsk). Sometimes 'Midland Norwegian' (midlandsmål) and/or 'South Norwegian' (sørlandsk) are considered fifth or sixth groups.

The dialects are generally mutually intelligible, but differ significantly with regard to accent, grammar, syntax, and vocabulary. If not accustomed to a particular dialect, even a native Norwegian speaker may have difficulty understanding it. Dialects can be as local as farm clusters, but many linguists note an ongoing regionalization, diminishing, or even elimination of local variations.

Spoken Norwegian typically does not exactly follow the written languages Bokmål and Nynorsk or the more conservative Riksmål and Høgnorsk, except in parts of Finnmark (where the original Sami population learned Norwegian as a second language). Rather, most people speak in their own local dialect. There is no "standard" spoken Norwegian.

Owing to geography and climate, Norwegian communities were often isolated from each other until the early 20th century. As a result, local dialects had a tendency to be influenced by each other in singular ways while developing their own idiosyncrasies. Oppdal Municipality, for example, has characteristics in common with coastal dialects to the west, the dialects of northern Gudbrandsdalen to the south, and other dialects in Sør-Trøndelag from the north. The linguist Einar Haugen documented the particulars of the Oppdal dialect, and the writer Inge Krokann used it as a literary device. Other transitional dialects include the dialects of Romsdal and Arendal.

On the other hand, newly industrialized communities near sources of hydroelectric power have developed dialects consistent with the region but in many ways unique. Studies in such places as Høyanger, Odda, Tyssedal, Rjukan, Notodden, Sauda, and others show that koineization has effected the formation of new dialects in these areas.

Similarly, in the early 20th century a dialect closely approximating standard Bokmål arose in and around railway stations. This was known as stasjonsspråk ("station language") and may have contributed to changes in dialect around these centers.

Until the 20th century, upward social mobility in a city like Oslo could in some cases require conforming speech to standard Riksmål. Studies show that even today, speakers of rural dialects may tend to change their usage in formal settings to approximate the formal written language. This has led to various countercultural movements ranging from the adoption of traditional forms of Oslo dialects among political radicals in Oslo, to movements preserving local dialects. There is widespread and growing acceptance that Norwegian linguistic diversity is worth preserving.

The trend today is a regionalisation of the dialects causing smaller dialectal traits to disappear and rural dialects to merge with their nearest larger dialectal variety.