Is there anyone out there? Astronomers have been pointing their radio telescopes at the skies for decades trying to pick up alien signals, so far without success. But now there's a new way of looking for aliens. Hitch a ride with Dr Graham Philips as he joins astronomers trawling through the galaxy looking for signs of extra-terrestrial intelligence.

The hunt for aliens is on! After a distinguished career in cosmology Professor Martin Rees, the astronomer royal, has taken up the search for extra-terrestrials. Looking for aliens is no longer science fiction - it is a question that's engaging some of the greatest minds in science." As our knowledge of the universe has increased, we're getting closer to answers. Many scientists now think we live in galaxy with a billion Earth-like planets, many of which may be teeming with life. But what kind of life? Has anything evolved into beings we could communicate with? This film gets inside the minds of the scientists considering one of the most exciting and profound questions we can ask - are we alone in the universe? Professor Rees thinks we may have our idea of what an alien is like all wrong. If he's right, it's not organic extra-terrestrials we should look for, it's machines.

Is mankind alone, or are there aliens out there, either waiting to be discovered, or on their way to find Earth? Professor Brian Cox spends this episode asking such questions, and what he discovers may raise a few eyebrows. He begins by exploring the human race's efforts to find neighbours in outer space, including the launch of two golden discs containing a greeting from Earth in the 1970s; they are still travelling and are now the most distant man-made objects from the planet. Brian also meets members of the Search for Extra-Terrestrial Intelligence, who have been monitoring radio signals for 50 years without success, before discussing the ingredients needed to make an intelligent civilisation with astrophysicist Dr Frank Drake.

In the third episode, the discovery of extraterrestrial life might face an impossible challenge: the physics of the universe itself; but using cutting-edge tech, experts might be on the verge of a groundbreaking find -- and the evidence could already be in hand.

What if aliens landed on Earth? Much of science fiction explores the moment of first contact – what will people do when the aliens land? From H. G. Wells’ pioneering The War of the Worlds to Independence Day, Men in Black, and District 9, Invasion deals with our fears of alien invasions of earth. David Tennant explains the appeal of Doctor Who’s Daleks and Cybermen while John Carpenter and Chris Carter explore the rich appeal of the paranoia fuelled by hidden aliens with The Thing and The X-Files. It also asks, what if the monsters were our own creation? With the aid of rarely seen animation tests, Phil Tippett takes us behind the scenes in the creation of the dinosaurs of Jurassic Park. But not all invasions are hostile. Peter Coyote and Richard Dreyfuss discuss the creation of Spielberg’s spellbinding classics E.T. the Extra-Terrestrial and Close Encounters of the Third Kind. There is more than one kind of invasion.

In August 1977, the Big Ear Radio-telescope in Ohio received a strange signal from the Sagittarius constellation while searching for intelligent extra-terrestrial life. It had a duration of 72 seconds and an intensity 30 times higher than usual. Named the Wow signal, it is still being considered as one of the best examples of having being sent by intelligent extraterrestrial life. But, nothing has revolutionised the search of extra-terrestrial intelligent life as much as the recent discovery by the Kepler Satellite, of thousands of Earth-like planets where life could be possible. Join the debate with this stunning documentary, as we ask Is Anybody Out There?