Famous faces, including Sienna Miller, say they believe newspaper reporters illegally listened to their mobile phones messages to try to get a scoop.
And they've decided to take The News of the World newspaper to court.
Investigations first started more than three years ago when a reporter was caught trying to listen in on members of the royal family to find stories.
The owners of the paper say they've always given police all the information they have and sacked anyone involved.
But Metropolitan police detectives have now launched a new inquiry into allegations of phone hacking at the News of the World.