If you're flying abroad for a holiday you could be in for a long wait as there are huge delays at UK airports.
On Thursday police stopped a terrorist plan to blow up 10 planes during flights from the UK to the US.
As a result security at UK airports is very high, and no-one can take any hand luggage onto planes. That includes things like games consoles and books.
Police have said they are confident they have stopped the terrorists' plan and are questioning 24 people.
What is allowed on board
Wallets, purses. passports, plane tickets
Travel documents essential for the journey
Medicines needed for the flight (eg, diabetic kit or inhalers)
Glasses and sunglasses, without cases
If you have a baby brother or sister your parents can take food and milk on board as long as they taste it in front of airport staff
Nappies and nappy cream
Tissues (unboxed) and/or handkerchiefs
Keys (but no electrical key fobs)
All passengers must be hand searched, and their shoes and all the items they are carrying must be X-rayed
Police have evacuated homes in High Wycombe, Bucks, following raids overnight.
It is thought that the plot involved taking explosives on board hidden in hand luggage and then using them to blow up planes in mid-flight.
As many as 10 planes may have been targeted.
The security threat level in the UK is at its highest at the moment - critical. This means another attack could happen at any time.
The police aren't aware of a particular planned attack, but need to be ready in case one is planned.
Only planes already in the air and on their way to Heathrow at the moment will be allowed to land. A number of flights scheduled to fly out of Heathrow have been cancelled.