Pilsen is a city in the Czech Republic. About 90 kilometres (56 miles) west of Prague in western Bohemia, it is the fourth most populous city in the Czech Republic with about 175,000 inhabitants.

The city is known worldwide for Pilsner beer, created by Bavarian brewer Josef Groll here in 1842. In 1375 Bohemian king Charles IV endowed the Dobrow Monastery near Plzen with the beer right, and it is one of the oldest breweries to survive to modern times. Many breweries were located in the interconnected deep cellars of the city.

The officials of Plzen founded a city-owned brewery in 1839, Bürger Brauerei (Citizens' Brewery, now Plzenský Prazdroj), and recruited Bavarian brewer Josef Groll (1813-1887) who produced the first batch of modern Pilsner beer on 5 October 1842. The combination of pale colour from the new malts, Pilsen's remarkably soft water, Saaz noble hops from nearby Žatec (Saaz in German) and Bavarian-style lagering produced a clear, golden beer which was regarded as a sensation. Improving transport meant that this new beer was soon available throughout Central Europe and Pilsner Brauart-style brewing was widely imitated.

In 1859, "Pilsner Bier" was registered as a brand name at the Chamber of Commerce and Trade in Plzen. In 1898, the Pilsner Urquell trade mark was created to put emphasis on it being the original brewery.

The most prominent sights of Plzen are the Gothic St. Bartholomew's Cathedral, founded in the late 13th century, whose tower, at 102 metres (335 feet), is the highest in the Czech Republic, the Renaissance Town Hall, and the Moorish Revival Great Synagogue, the second largest synagogue in Europe, after the Dohány Street Synagogue in Budapest. There is also a 20 km (12 mi) historic tunnel and cellar network, among the longest in Central Europe. Part of this network is open to the public for tours of about 750 metres (2,500 feet) in length and down to a depth of 12 m (39 ft).

Built in 1532, the former water tower was integrated into the city's fortification system at Prague Gate. Another storey was added in 1822 in French Imperial style. The Gothic portal dating from the 1500s and coming from another house, which had been demolished, was added in 1912. Above the portal there is a commemorative plaque dedicated to Dr Josef Škoda (a professor at the Vienna University), who was born next door on 10 December 1805.

Plzen is also well known for the Pilsner Urquell (since 1842) and Gambrinus (since 1869) breweries, currently owned by Asahi Group Holdings. A popular tourist attraction is the Plzensky Prazdroj brewery tour where visitors can discover the history of beer. The pilsener style of beer was developed in Plzen in the 19th century.

Plzen was a European Capital Of Culture in 2015, along with Mons in Belgium.