Cieszyn Silesia (Cz. Těšínské Slezsko, Ger. Teschener Schlesien) is a historical region in Poland and the Czech Republic, covering the south-eastern part of Silesia around the town of Cieszyn and the river Olza. Its area is about 2280 km², with a population of over 800,000 people (463,000 on the Czech and about 350,000 people on the Polish side). The boundaries of the region formed with the rise of Cieszyn castellany, mentioned for the first time in 1155. Then the region became a duchy, which since 15th c. began to lose temporarily or permanently its territorial unity, even though, the inhabitants maintained the sense of togetherness among themselves for a long time.
In some of the literature, Cieszyn Silesia and Upper Silesia are treated as two separate regions, and according to other works Cieszyn Silesia is located in the historical and geographical boundaries of Upper Silesia. Residents of Cieszyn Silesia are characterized by a very strong sense of regional identity, this applies to both the Polish part of the region, as well as the so-called Zaolzie ('area beyond the Olza River'). One of the distinctive features of the region was the great development of the Polish national movement.
Geographically, to Cieszyn Silesia belong: the western part of the Silesian Foothills (also called Cieszyn Foothills), the western part of the Silesian Beskids (border ran along the Wisła and Soła watershed), the eastern part of the Silesian-Moravian Beskids, the northern part of the Moravian Gate and south-western part of the Oświęcim Basin. The main rivers are: Olza , Wisła (Vistula), Ostrawica, Odra (Oder), Biała. The highest peaks include: