Frankfurt am Main (/ˈfræŋkfərt/; German: [ˈfʁaŋkfʊʁt ʔam ˈmaɪn] ^ⓘ;^[5][6] lit. "Frank ford on the^[a] 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.^[b] Located in the foreland of the Taunus on its namesake Main, it forms a continuous conurbation with Offenbach am Main; its urban area has a population of over 2.7 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.

Frankfurt was a city state, the Free City of Frankfurt, for nearly five centuries, and was one of the most important cities of the Holy Roman Empire, as a site of Imperial coronations; it lost its sovereignty upon the collapse of the empire in 1806, regained it in 1815 and then lost it again in 1866, when it was annexed (though neutral) by the Kingdom of Prussia. It has been part of the state of Hesse since 1945. Frankfurt is culturally, ethnically and religiously diverse, with half of its population, and a majority of its young people, having a migrant background. A quarter of the population consists of foreign nationals, including many expatriates. In 2015, Frankfurt was home to 1,909 ultra high-net-worth individuals, the sixth-highest number of any city. As of 2023, Frankfurt is the 13th-wealthiest city in the world and the second-wealthiest city in Europe (after London).

Frankfurt is a global hub for commerce, culture, education, tourism and transportation, and is the site of many global and European corporate headquarters. Due to its central location in the former West Germany, Frankfurt Airport became the busiest in Germany, one of the busiest in the world, the airport with the most direct routes in the world, and the primary hub for Lufthansa, the national airline of Germany and Europe's largest airline. Frankfurt Central Station is Germany's second-busiest railway station after Hamburg Hbf, and Frankfurter Kreuz is the most-heavily used interchange in the EU. Frankfurt is one of the major financial centers of the European continent, with the headquarters of the European Central Bank, Deutsche Bundesbank, Frankfurt Stock Exchange, Deutsche Bank, DZ Bank, KfW, Commerzbank, DekaBank, Helaba, several cloud and fintech startups, and other institutes. Automotive, technology and research, services, consulting, media and creative industries complement the economic base. Frankfurt's DE-CIX is the world's largest internet exchange point. Messe Frankfurt is one of the world's largest trade fairs. Major fairs include the Music Fair and the Frankfurt Book Fair, the world's largest book fair. With 108 consulates, among which the largest is the US Consulate General, Frankfurt is second to New York City among non-capital cities in regards to consulate seats.

Frankfurt is home to influential educational institutions, including the Goethe University with the Universitätsklinikum Frankfurt (de) (Hesse's largest hospital), the FUAS, the FUMPA, and graduate schools like the FSFM. The city is one of two seats of the German National Library (alongside Leipzig), the largest library in the German-speaking countries and one of the largest in the world. Its renowned cultural venues include the concert hall Alte Oper, continental Europe's largest English theater and many museums, 26 of which line up along the Museum Embankment, including the Städel, the Liebieghaus, the German Film Museum (de), the Senckenberg Natural Museum, the Goethe House and the Schirn art venue. Frankfurt's skyline is shaped by some of Europe's tallest skyscrapers, which has led to the term Mainhattan. The city has many notable green areas and parks, including the Wallanlagen, Volkspark Niddatal, Grüneburgpark, the City Forest, two major botanical gardens (the Palmengarten and the Botanical Garden Frankfurt) and the Frankfurt Zoo. Frankfurt is the seat of the German Football Association (Deutscher Fußball-Bund – DFB), is home to the first division association football club Eintracht Frankfurt, the Löwen Frankfurt ice hockey team, and the basketball club Frankfurt Skyliners, and is the venue of the Frankfurt Marathon and the Ironman Germany.