A transit visa may be required when you pass through one country to reach another. Most travellers have no issue, but the wrong ticket combination can mean being denied boarding and losing the fare.
The rule depends on your nationality, the visas you already hold, the transit country and whether you leave the airport.
What is a transit visa?
A transit visa lets you pass through a country without staying. An airport transit visa (type A in Schengen) covers a connection within the international transit area. If you enter the country, for example to travel overland or reach another airport, you need a regular short-stay visa (type C).
Do you need a visa for a connecting flight?
Usually not if you stay in the international transit area. You do need an entry visa if you must collect and re-check baggage, pass border control to change terminals, change airports or want to go into the city.
With separately booked tickets, baggage is often not checked through, which is the most common transit problem.
Who needs an airport transit visa?
Schengen states require it from nationals on a common list, and each member state can add countries to its own list, so a visa not needed in one Schengen country may be needed in another.
For Turkish citizens the rule depends on the transit country. Check the current list on that country’s foreign ministry or embassy page before booking.
Who is exempt?
Even where an airport transit visa applies, holders of a valid Schengen visa or residence permit, holders of valid visas or residence permits from countries such as the United States, Canada or Japan, and family members of EU citizens are generally exempt.
Conditions vary, so confirm the details with the official source.
How does transit work outside Schengen?
Every country has its own rule. The United States has no transit area, so every connecting passenger goes through entry and needs a transit (C-1) or valid visitor visa. The United Kingdom has separate visas for airside and landside transit.
What should you check before buying a ticket?
Check the transit rule for your nationality, whether the tickets are on one booking, whether baggage is checked through and whether the connection is at the same airport.
Airlines must refuse passengers without the required visa. If in doubt, get written confirmation from the airline or choose a direct flight.