The Duchy of Kuyavia (Polish: Księstwo kujawskie; Latin: Ducatus Cuiaviensis) was a district principality in Central Europe, created in the course of the 13th century in the region of modern-day Kuyavia after the inheritance of the Kingdom of Poland in 1138 into partial duchies through the will and testament of Duke Bolesław III Wrymouth.

Located between the regions of Greater Poland and Mazovia, it was the tribal area of the Goplans (Latin Glopeani, which roughly means "residents of Lake Gopło") with the political center in Kruszwica.

[2] In 1233 it became an independent duchy under Duke Casimir I, which, due to further divisions of inheritance (1267 and 1314), fragmented into the sub-duchies of Brześć, Inowrocław and Gniewkowo.

[3][4] After the unification of part of the Polish duchies to form the Kingdom of Poland under King Władysław I Łokietek, it lost its sovereignty after 1306 and became its vassal.

King Władysław II Jagiełło claimed the following territories in his title: Wladislaus dei gracia Rex Polonie, nec non terrarum Cracovie, Sandomirie, Siradie, Lancicie, Cuyauie, Lituanie princeps supremus, Pomeranie, Russieque dominus et heres, etc.