The Silesian tribes (Polish: plemiona śląskie) is a term used to refer to tribes, or groups of West Slavs that lived in the territories of Silesia in the Early Middle Ages. The territory they lived on became part of Great Moravia in 875 (now mostly in the Czech Republic) and later, in 990, the first Polish state created by duke Mieszko I and then expanded by king Boleslaw I at the beginning of the 11th century. They are usually treated as part of the Polish tribes and sometimes as part of the Germanic tribes. Two tribes among them are sometimes considered as Czech (Moravian) tribes.
Before and during the migration period the territory of south west Poland - Silesia - was inhabited by various peoples. It included Celts and probably some Germanic tribes - among them - the Silingi. Tacitus in his description of Magna Germania mentions Suevi: Marsigni, Osi, Gotini, Buri in what later became Silesia and Burgundiones and Lygii at the Vistula.
However, during the migration period, those peoples had moved west and vacated territories in Central Europe. Lands in the basins of Odra and Wisła were then taken by Polish tribes who repopulated these abandoned areas and created their own tribal organizations. The Silesian tribes, together with the Polans, Masovians, Vistulans and Pomeranians were the most important Polish tribes. These five tribes "shared fundamentally common culture and language and were considerably more closely related to one another than were the Germanic tribes."