Special helplines have been set up to support customers affected by the collapse of airline Monarch.
Passengers stranded abroad should call +44 1753 330330 from overseas while people in the UK can contact 0300 303 2800.
A dedicated website, monarch.caa.co.uk has also been set up with advice and information on flights back to the UK.
When will I be able to fly and when should I go to the airport?
Officials aim to deliver flights as close as possible to the existing departure dates, but no earlier.
Travellers are urged to prepare for disruption to journeys and arrive more than three hours before your confirmed new flight to be issued new details for check in.
There will be no online check-in as your previous booking details will be void.
Foreign Office staff will be available at affected airports to help any vulnerable British citizens with specific needs. Visit gov.uk/world for more details.
GTR honours rail tickets of Monarch passengers
Govia Thameslink Railway has said its three train companies that serve airports will all honour the rail tickets of Monarch passengers returning to the UK early or late.
This applies to passengers with advanced pre-dated rail tickets returning from Luton (with Thameslink) and Gatwick (with Gatwick Express, Southern and Thameslink).
Will I have to pay for the flight or extra accommodation?
You will not be asked to pay for your flight yourself - but will have to provide details of your original Monarch booking once on board the plane.
If you are not Atol (Air Travel Organiser's Licence) protected, this will allow the Government to claim the cost of their replacement flight directly from your credit or debit card company.
Passengers with Atol protection are entitled to reasonable accommodation and subsistence costs if they are delayed by more than four hours.
Those without Atol protection may be able to claim from credit card providers or insurers.
The Civil Aviation Authority will process your refund as quickly as possible.
To see if you are Atol protected, check if you have received a certificate or ask your travel agent.
I've got a future booking, what should I do?
Check monarch.caa.co.uk or a travel agent, if you booked with one, regarding all future bookings.
They will be able to see if you can change your holiday booking or are entitled to a refund or compensation.
If you are not covered by the Atol scheme, you should also contact your credit card company or travel insurer.