| Native Name: | Księstwo kujawskie (Polish) Ducatus Cuiaviensis (Latin) |
| Conventional Long Name: | Duchy of Kuyavia |
| Common Name: | Kuyavia |
| Era: | High Middle Ages |
| Status: | Independent state |
| Government Type: | District principality |
| Life Span: | 1233–1392 |
| Event Start: | Separation from the Duchy of Masovia |
| Date Start: | 1233 |
| Event End: | Partition into duchies of Inowrocław and Brześć Kujawski |
| Date End: | 1392 |
| P1: | Duchy of Masovia |
| Flag P1: | Chorągiew księcia mazowieckiego Siemowita.svg |
| Border P1: | no |
| S1: | Duchy of Inowrocław |
| Flag S1: | POL województwo brzeskokujawskie IRP COA.svg |
| Border S1: | no |
| S2: | Duchy of Brześć Kujawski |
| Flag S2: | POL województwo brzeskokujawskie IRP COA.svg |
| Border S2: | no |
| S3: | Duchy of Łęczyca |
| Flag S3: | POL województwo łęczyckie IRP COA.svg |
| Border S3: | no |
| S4: | Duchy of Sieradz |
| Flag S4: | POL województwo sieradzkie IRP COA.svg |
| Border S4: | no |
| Religion: | Roman Catholic |
| Image Map Caption: | Duchy of Kuyavia within Kingdom of Poland in 13th century. |
| Capital: | Inowrocław |
| Today: | Poland |
| Official Languages: | Polish, Latin |
| Title Leader: | Duke |
| Leader1: | Casimir I of Kuyavia |
| Year Leader1: | 1233–1267 |
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. It was connected to Greater Poland from the 10th century, and to the Duchy of Masovia from 1138.[1] In 1231, the duchies of Sieradz and Łęczyca, had been formed from a part of the state.[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. In the Polish–Teutonic War, the sparsely populated area of the duchy was occupied by the Teutonic Order in 1332. The Teutonic Order returned the duchy to the Polish crown in the Peace Treaty of Kalisz (1343).
The duchy was confiscated as a settled fiefdom by the Polish crown towards the end of the 14th century and was given direct administrative control in the kingdom in the course of the 15th century in the form of two incorporated voivodships (with seats in Brześć Kujawski and Inowrocław with a joint local state parliament (Sejmik) in Radziejów). The area belonged to Poland until the Partitions (1772, 1793, 1795).
In the following centuries, the memory of the duchy was only preserved in the names of the voivodeships and in the titulary of the Polish rulers. 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.