This no-nonsense guide to one of our most enduring mysteries presents a short history of the strangest encounters, looks carefully at explanations from the blunt to the truly bizarre, offers insights into the strongest evidence that we are being visited by beings from another world and sources the best sceptical arguments that it can all be explained rationally. Concise, balanced and - occasionally - hilarious this is a story that has as much to tell you about the human race as it does about aliens.