Slovincian is the language formerly spoken by the Slovincians (German: Slowinzen, Lebakaschuben), a Slavic people living between lakes Gardno (Gardersee) and Łebsko (Lebasee) near Słupsk (Stolp) in Pomerania.

Slovincian is classified either as a language (first by Friedrich Lorentz, 1902/3), or as a Kashubian dialect (first by Lorentz, after 1903) or variant, with Kashubian itself being classified either as a language or a Polish dialect. Slovincian and Kashubian are both classified as Pomeranian.

Slovincian became extinct in the early twentieth century. However, individual words and expressions survived until after World War II, when the region became Polish. Some Slovincians were expelled along with the Germans, of those allowed to stay a few elderly people had fragmentary knowledge of Slovincian until the 1950s.

It is disputed whether Slovincians actually used that name, given to them by the Russian academic Aleksander Hilferding, for themselves. Lebakaschuben is a synonymously used term. Some scholars believe that Slovincians regarded themselves merely as Lutheran Kashubians and their language as Kashubian. Nevertheless, the name "Slovincian" prevails in literature and is also used officially, for example in Słowiński Park Narodowy (Slovincian National Park), a protected area on the Polish Pomeranian coast.