|Script:||Latin (Kashubian alphabet)|
|Nation:||In official use, as a regional language, in some communes of Pomeranian Voivodeship, Poland|
|Agency:||Kashubian Language Council|
Kashubian or Cassubian (Kashubian: kaszëbsczi jãzëk, pòmòrsczi jãzëk, kaszëbskò-słowińskô mòwa; Polish: język kaszubski, język pomorski, język kaszubsko-słowiński) is one of the Lechitic languages, a subgroup of the Slavic languages.  
Kashubian is assumed to have evolved from the language spoken by some tribes of Pomeranians called Kashubians, in the region of Pomerania, on the southern coast of the Baltic Sea between the Vistula and Oder rivers.
It is closely related to Slovincian, and both are dialects of Pomeranian. Many linguists, in Poland and elsewhere, consider it a divergent dialect of Polish, although now it is usually recognized as the closest living relative of Polish. The Polish Wikipedia article on Kashubian contains a thorough discussion of this question. Dialectal diversity is so great within Kashubian that a speaker of southern Kashubian has considerable difficulty in understanding a speaker of the northernmost dialects.
Like Polish, Kashubian includes about 5% loanwords from Low German, such as kùńszt (art), and some from High German. Other sources of loanwords include the Baltic languages, Russian and Polish. In dialects of Kashubian a schwa occurs.
The earliest printed documents in Kashubian date from the end of the 16th century. The modern orthography was first proposed in 1879.
In the 2002 census, 53,000 people in Poland declared that they mainly use Kashubian at home. All Kashubian speakers are also fluent in Polish. A number of schools in Poland use Kashubian as a teaching language. It is an official alternative language for local administration purposes in Gmina Sierakowice and Gmina Parchowo in Pomeranian Voivodeship. Kashubian is also spoken by Kashubians living in Canada.
Important for Kashubian literature was Xążeczka dlo Kaszebov by Doctor Florian Ceynowa (1817–1881). Hieronim Derdowski (1852-1902 in Winona, Minnesota) was another significant author who wrote in Kashubian, as did Doctor Aleksander Majkowski (1876–1938) from Kościerzyna. Jan Trepczyk was a poet who wrote in Kashubian, as was Stanisław Pestka. Kashubian literature has been translated into Czech, Polish, English, German, Belarusian, Slovene and Finnish. A considerable body of Christian literature has been translated into Kashubian, including the New Testament, much of it by Fr. Adam Ryszard Sikora (OFM). Rev. Franciszek Grucza graduated from a Catholic seminary in Pelplin. He was the first priest to introduce Catholic liturgy in Kashubian language.
There were school strikes by Kashubian children in 1906. Following the collapse of Communism in Poland, attitudes on the status of Kashubian have been gradually changing. It is increasingly seen as a fully-fledged language, since it is taught in state schools and has some limited usage on public radio and television. Since 2005 Kashubian has enjoyed legal protection in Poland as an official regional language. It is the only language in Poland with this status, which was granted by an act of the Polish Parliament on January 6, 2005. The act provides for its use in official contexts in ten communes where Kashubian speakers constitute at least 20 percent of the population.