The Altstadt is a quarter of Frankfurt am Main, Germany. It is part of the Ortsbezirk Innenstadt I and is located on the northern Main river bank. It is completely surrounded by the Innenstadt district, Frankfurt's present-day city centre. On the opposite side of the Main is the district of Sachsenhausen.

Frankfurt am Main is the most populous city in the German state of Hesse. Its 773,068 inhabitants as of 2022 make it the fifth-most populous city in Germany, and it is the only city in the country rated as an "alpha world city" according to GaWC. Located in the foreland of the Taunus on its namesake Main, it forms a continuous conurbation with the neighbouring city of Offenbach am Main and its urban area has a population of over 2.3 million. The city is the heart of the larger Rhine-Main metropolitan region, which has a population of more than 5.8 million and is Germany's second-largest metropolitan region after the Rhine-Ruhr region and the fourth biggest metropolitan region by GDP in the European Union. Frankfurt is home to the European Central Bank, one of the institutional seats of the European Union, while Frankfurt's central business district lies about 90 km (56 mi) northwest of the geographic center of the EU at Gadheim in Lower Franconia. Like France and Franconia, the city is named after the Franks. Frankfurt is the largest city in the Rhenish Franconian dialect area.