Whether you need a visa for a 10-hour transit in Frankfurt depends entirely on your nationality and whether you intend to leave the airport. If you are a citizen of a country with a visa-waiver agreement with the EU (like the US, UK, Canada, or Australia), you do not need a visa; you can even exit the airport and visit the city. If you are from a country that requires a Schengen Visa, you normally need an Airport Transit Visa (ATV) just to stay in the international transit area. However, if your layover is 10 hours and you wish to go into Frankfurt to see the "Römerberg" or have lunch, you would need a full Schengen C Visa to pass through immigration. It is important to note that in 2026, the ETIAS (European Travel Information and Authorisation System) is mandatory for visa-exempt travelers; you must have this digital authorization to enter the country, even for a few hours. Always check your specific passport requirements, as some nationalities (like Indian or Turkish citizens) have very specific "transit-only" rules at German airports.