Mannheim (ˈmanhaɪm; Palatine German: Mannem or Monnem), officially the University City of Mannheim (Universitätsstadt Mannheim), is the second-largest city in the German state of Baden-Württemberg, after the state capital of Stuttgart, and Germany's 21st-largest city, with a 2021 population of 311,831 inhabitants. The city is the cultural and economic centre of the Rhine-Neckar Metropolitan Region, Germany's seventh-largest metropolitan region with nearly 2.4 million inhabitants and over 900,000 employees.
Mannheim is located at the confluence of the Rhine and the Neckar in the Kurpfalz (Electoral Palatinate) region of northwestern Baden-Württemberg. The city lies in the Upper Rhine Plain, Germany's warmest region. Together with Hamburg, Mannheim is the only German city bordering two other federal states. It forms a continuous conurbation of around 480,000 inhabitants with Ludwigshafen am Rhein in the neighbouring state of Rhineland-Palatinate, on the other side of the Rhine. Some northern suburbs of Mannheim belong to Hesse. Upstream along the Neckar lies Heidelberg, the fifth-largest city of Baden-Württemberg and the third-largest of the Rhine-Neckar Region.
Mannheim is unusual among German cities in that its city centre streets and avenues are laid out in a grid pattern, leading to city's nickname Quadratestadt (Square City). Within a ring of avenues surrounding the city centre, there are squares, numbered from A1 to U6, instead of street names. At the southern base of that system is Mannheim Palace, one of the largest palace complexes in the world, and the second-largest in Baroque style after Versailles. It was the former home of the Prince-elector of the Electoral Palatinate, and now houses the University of Mannheim, which repeatedly receives top marks in business administration and is sometimes known as the "Harvard of Germany". The Mannheim May Market is the largest regional consumer exhibition of Germany. The civic symbol of Mannheim is the Romanesque Mannheim Water Tower, completed in 1886 and rising to above the highest point of the art nouveau area Friedrichsplatz.