Watch Sonali's report
People who don't want a third runway at London's Heathrow Airport have won an important battle to try to stop it being built.
The government says the runway is needed to cope with the number of people flying in and out of London.
But a lot of family homes would need to be demolished, and environmental experts say that the extra planes will cause loads more pollution.
Now a judge at the High Court said he also disagrees with the runway plans.
The decision comes just over a year after the government agreed to plans for the third runway.
Campaigners who don't want it built cheered when they heard the judge's decision, but they can't totally relax.
A new runway could still go ahead, but the government needs to rethink its ideas and come up with a better way to prove that making Heathrow bigger really is a good idea.