Piața Unirii (Romanian pronunciation: [ˈpjat͡sa uˈnirij], Union Square) is the largest square in central Bucharest, Romania, and one of the largest public spaces in Europe, being located in the center of the capital where Sectors 1, 2, 3, and 4 meet. Part of the Civic Centre, it is bisected by Unirii Boulevard, originally built during the Communist era as the Boulevard of the Victory of Socialism, and renamed after the Romanian Revolution of 1989.

The square is a significant transportation hub, containing the Piața Unirii metro station and a major interchange for STB buses; there is also a tram terminal near the southwest corner. The Unirea Shopping Center, the Cocor department store and a large taxi stand are located on the east side of this square, while the historic Hanul lui Manuc is on the north side, near the northeast corner. The centre of the square boasts a park and the fountains which are particularly popular with commuters and passers-by in the torrid summer months, as it is the largest complex of fountains in Europe and one of the most impressive in the world, its spectacle becoming a huge tourist attraction after the reopening of the fountains in 2018, as part of the celebrations of the Centennial of the Great Union of 1918. There were plans since the interwar period to build the Romanian National Salvation Cathedral on the place of this park, but in the early 2000s the idea proved technically impossible due to the busy underground environment and therefore the location was changed.

In 2023, an analysis carried out by civil engineers revealed severe degradation to the cover of the Dâmbovița River at Piața Unirii. The cover, which was part of a larger, unrealized project between 1938 and 1941, was found to be in a state of advanced degradation, with exposed rebar and crumbling concrete. Following these revelations, traffic of over 3.5 tonnes is banned from travelling through the square.

• Centrul Civic

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  Unirea Shopping Center
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  Fountains in the center of Unirii Square
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  Splaiul Independenței
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  Bulevardul Unirii passing through Piața Unirii
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  National Library and the Dâmbovița River as seen from Piața Unirii

44°25′40.79″N 26°6′7.82″E / 44.4279972°N 26.1021722°E / 44.4279972; 26.1021722