Bielsko-Biała (Polish: [ˈbjɛlskɔ ˈbjawa] ; Czech: Bílsko-Bělá; German: Bielitz-Biala, Silesian: Biylsko-Biołŏ; Wymysorys: Byłc-Bejł) is a city in southern Poland, with a population of approximately 166,765 as of December 2022, making it the 22nd largest city in Poland, and an area of 124.51 km2 (48.07 sq mi). It is the core of the broader metropolitan area with around 335,000 inhabitants. It serves as the seat of the Bielsko County, Euroregion Beskydy, Roman Catholic Diocese of Bielsko–Żywiec and the Evangelical Church Diocese of Cieszyn.
Situated north of the Beskid Mountains, Bielsko-Biała is composed of two former towns which merged in 1951—Bielsko in the west and Biała in the east—on opposite banks of the Biała River that once divided Silesia and Lesser Poland. The history of Bielsko dates back to the 13th century, while Biała was founded in the 16th century and obtained city rights in 1723. Despite the administrative separation, both towns effectively functioned as one urban area already in the 19th century. Industrialization, especially the textile and automotive industries, was of great importance for its development in the past. Between 1975 and 1998, the city was the seat of Bielsko-Biała Voivodeship and currently lies within the Silesian Voivodeship.
Bielsko-Biała is the administrative, economic, academic and cultural centre for the Silesian-Lesser Polish border region, sometimes colloquially referred to as Podbeskidzie. It is also an important commercial and industrial hub, as well as a road and railway junction. It is a significant tourist destination due to its numerous architectural monuments (a popular slogan Little Vienna refers to many Revivalist and Art Nouveau buildings shaping the cityscape of the central districts) and its direct proximity to the mountains (fourteen mountain peaks lie within the city limits).