Mannheim, officially the University City of 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 2020 population of approximately 309,119 inhabitants. The city is at the centre of the Rhine-Neckar Metropolitan Region, Germany's eighth-largest metropolitan region.
Mannheim is located at the confluence of the Rhine and the Neckar in the Kurpfalz region of northwestern Baden-Württemberg. The city lies in the Upper Rhine Plain, Germany's warmest region. Together with Hamburg, Mannheim is the only 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 already belong to Hesse. Upstream along the Neckar lies Heidelberg, the third-largest city of the Rhine-Neckar Region.
Mannheim is unusual among German cities in that its streets and avenues are laid out in a grid pattern, leading to its nickname Quadratestadt.