SETI uses radio telescopes to listen for signals which may be transmitted from other civilizations. Many believe that our first contact with extraterrestrials will occur by picking up their radio transmissions. This makes sense to us, afterall, it's a lot more efficient (and easier) to search for and contact other advanced life forms by transmitting signals than by physically traveling billions of miles to thousands of planets. To learn more, visit SETI's web site, below.