I believe they exist. But whether they are from another planet, another dimension or if they somehow live side by side with us is hard to tell. Also, I don't think they are that smart, but they have some way of manipulating us.
Oh right, I guess my information was kind of fuzzy. Although I could've sworn I heard something about scientists having found organisms similar to bacteria and the like, but just now I looked at Wikipedia and it looks like they only found indirect evidence of them in Mars. But yes, that definitely doesn't rule out the possibility of advanced alien life (even if they're among us)!@Vin The Dreamer Mars used to carry water back when it had an atmosphere, but over the years it's atmosphere worn down to the point where it could no longer maintain the water. Causing the water to evaporate (the state of matter an object is in is also due to pressure as well as temperature.) So there is no water on the surface of Mars, but there can be water be water underground.
As of right now, no scientist haven't found any life. There are places where their can be life, and there are signs for life, but no solid life forms have been found outside of Earth.
Well that's the science side, I personally believe that there is Alien life and they are even living with us. Play nicely, because I'm sure even Aliens have feelings.