Lots of films have been released in 2009 in 3D, with the latest the animated guinea pig movie G-Force.
3D films have been around for a while but they've really taken off recently thanks to new technology.
It often costs extra to watch 3D films. Cinemas say that's because they have to buy new projectors to show them.
Some people in the film world think that it's not worth paying more money to watch them, and film companies should stick to making 2D films.
But the people who make the films say it's a really exciting way of watching new movies.
Some film companies say that all their animations will now be made in 3D, and lots more live-action films will be too.
3D is big news, and recently Newsround has done lots of reports on films, video games, webcams and even lessons using the technology!