The article provides an overview of the lexical and grammatical features as well as the sociopolitical environment of Marollien that originated in the 18th century as a dialect on the territory of Brussels. Marollien is essentially the Dutch language in its Brabantian dialect, strongly influenced by French. There are literary works, performances, and musicals written and staged in Marollien, as well as dictionaries and journals published in it. Historically, the Marollien dialect is a sociolect: it was generally used by Belgians coming to Brussels from Wallonia in search of a job and settling in one of the districts of Brussels — Marolles. A special emphasis is placed on lexical features of the dialect: gastronomic and everyday vocabulary are looked at and the examples of French loanwords and Southern Dutch language norm deviations are provided. Standard Dutch calques in French, when translating idioms in particular, are also identified. The differences between Dutch, French, and Marollien place names are illustrated. In the field of morphology and word formation, there is a regular mixture of Germanic and Romanic stems which is indicated. Examples of Marollien phonetic features are also provided. The article acknowledges frequent code switching in Marollien speech, which by and large resembles the phenomenon of linguistic interference. Due to the fact that Marollien is rapidly disappearing, the Brussels-Capital region is trying to support the dialect: various activities are being organized in order to propagate its use and enhance its prestige. Nevertheless, Marollien is not included in the well-known citizen initiative “Marnix Plan”, aimed at developing the methodology for the sequential study of several languages for all segments of the population in Brussels. This initiative is also discussed in the article.