Mainz is the capital and largest city of the German state of Rhineland-Palatinate, and with around 221,000 inhabitants, it is Germany's 35th-largest city. It lies in the Rhine-Main Metropolitan Region—Germany's second-largest metropolitan region after Rhine-Ruhr—which also encompasses the cities of Frankfurt am Main, Wiesbaden, Darmstadt, Offenbach am Main, and Hanau.

Rhineland-Palatinate is a western state of Germany. It covers 19,846 km2 (7,663 sq mi) and has about 4.05 million residents. It is the ninth largest and sixth most populous of the sixteen states. Mainz is the capital and largest city. Other cities are Ludwigshafen am Rhein, Koblenz, Trier, Kaiserslautern, Worms and Neuwied. It is bordered by North Rhine-Westphalia, Saarland, Baden-Württemberg and Hesse and by France, Luxembourg and Belgium.