The Science Museum in London is launching a new exhibition called The Science of Aliens.
It explores the possibility of aliens using famous characters from movies, books, TV and scientific evidence.
It also looks at the many myths behind extra-terrestials.
So we want to know if YOU believe in aliens?
Do you think there are life forms living on other planets?
Are reports of alien sightings genuine?
Or are people letting their imaginations run wild?
E-mail and let us know.
Unfortunately this topic is now closed but there are Comments pages on other subjects on the main Chat index.
Yes, becuse one night I saw a big red flash in the sky and then it vanished!
Mathew, 13, Llanelli
I totally think that aliens are real. After all my best friend behaves like one!!!!!
Tasha, 11, Brighton
I think there has to be life on other planets.
Cameron, 13, Methil
Some people say they have been abducted and probed by aliens but there is never seems to be any proof.
David, 12, Marbella
Sure there are aliens. Maybe some sort of ant or something. Maybe even a sort of human type thing but not those classic black eyed green people from mars - that's a fairy tale!
Ann, 12, East Anglia
I would like to believe in aliens, but I don't think that there are life forms that are as intelligent as us. They might even be insect-like or something!
Ruby, 12, Saffron Waldon
I do not believe in aliens.
Cameron, 8, Bamford
I don't. They're only used in films, books and all that and I wouldn't believe a person saying they saw an alien.
Kate, 14, Manchester
In the vastness that is space there has to be some other intelligent beings somewhere. It's just a shame that there are none down here.
Sonny, 14, Geneva
I think one day they will come and they will not look like what we expected - the earth will be flabbergasted!
Megan, 13, Glasgow
There's got to be something else apart from us! The universe is big enough! We even had one science lesson where the title and subject was: Are we alone?
Immy, 12, Tunbridge Wells
Yea, I totally believe that there is life on other planets. Aliens Rock!!
Fifi, 14, Javea
I guess we'll never know but we're a unique planet that can support a type of life the same as ours. I doubt that there are any other life forms like us, but there might be types of animals.
Jamie, 13, Newcastle
Aliens have been with us for decades. Where do you think the Americans get their plane ideas from?
Rey, 12, Australia
I do sometimes but then sometimes I don't. I think to myself that there must be aliens but then I think I'm being silly - ther are too many theories to make a decision!
Michelle, 14, Huddersfield
I find it very difficult to believe earthlings are the only life forms in the universe!
Kath, 14, Chelsea