Colognian or Kölsch (pronounced [kœ̂lɧ], narrower [kœ̂ɫːʃ]^ⓘ; full name Kölsch Platt) is a small set of very closely related dialects, or variants, of the Ripuarian group of dialects of the Central German group. These dialects are spoken in the area covered by the Archdiocese and former Electorate of Cologne reaching from Neuss in the north to just south of Bonn, west to Düren and east to Olpe in northwest Germany.

In the Ripuarian dialects, "kölsch" is an adjective meaning 'from Cologne' or 'pertaining to Cologne', thus equivalent to "Colognian". Its nominalized forms (ene Kölsche, de Kölsche etc.) denote the inhabitants of Cologne. The word "Kölsch", without an article, refers to either the dialect or the local Kölsch beer. Hence the humorous Colognian saying: "Ours is the only language you can drink!"

In Cologne, it is actively spoken by about 250,000 people, roughly one quarter of the population. Almost all speakers are also fluent in standard or high German. It is widely understood in a region inhabited by some 10 million people (a conservative estimate).

There was a community of people who spoke a variety of Kölsch in Dane County, Wisconsin, United States.

There are local (decreasingly divergent) variants of Kölsch in the Quarters, most notably those only recently incorporated into the city, and the Hinterland.^{[clarification needed]} Sometimes, also the far more than 100 clearly distinct Ripuarian languages of Belgium, the Netherlands, and German Rhineland are incorrectly referred to as Kölsch, as well as the Rhinelandic regiolect. In fact, the regiolect is very different from Kölsch, being the regional variety of Standard German influenced only to a certain degree by the dialect. As such, many native speakers of the regiolect are in fact unaware of the fact that a “regiolect” exists, believing they speak plain Standard German.^{[citation needed]}

In its modern form, it is of comparatively recent origin. It developed from Historic Colognian, but has been under the influence of New High German since the 17th century. It was also influenced by French during the occupation of the Left Bank of the Rhine under Napoleon Bonaparte from 1794 to 1815, and therefore contains some more words from and expressions pertaining to French than does Standard German. There are also phonological similarities with French, which however may be coincidental.

Kölsch is one of the variants of the Ripuarian dialects (not part of the Rhinelandic regiolect, rheinisch), which belong to West Middle German family. It is closely related to the lower Rhineland (niederrheinisch) and Moselle Franconian (moselfränkisch) dialects and combines some features of them, as well employing a variety of words hardly in use elsewhere. Common with the Limburgish language group and other Ripuarian languages, it has a phonemic pitch accent, referred to as the 'singing' Rhinelandic tone.

This list shows only the most important differences. Most of these are not uniquely Kölsch, but true for all Ripuarian dialects.