If extraterrestrial beings do exist, they have probably already visited our world throughout the past and continue to observe our human development today. The life-forms and/or their spacecraft could be merely a product of vivid imaginations, unusual effects created by atmospheric conditions, astronomical phenomena, or even arising from supernatural causes... However this explanation is unconvincing in light of the many reported encounters that remain inexplicable. This book traces the progress of our intimate association with these perceived life-forms and their aerial craft, commencing from their earliest potential contacts with several ancient civilisations and subsequent development of various mythological gods. Extraterrestrial: Alien Life studies the various unidentified/unconventional flying objects created by meteorological phenomena, as well as a raft of unusual craft of 'unknown/alien origin' and their extensive range of observed design and performance characteristics. Case studies of relevant alien landings, incursions and physical descriptions of various extraterrestrial beings are reviewed, as well as their probable innovative advanced technology, in order to provide a technical insight into these cosmic visitors. Extraterrestrial also looks at contemporary space exploration that aims to identify distant exoplanets with suitable biosignatures to sustain life. And this provides further guidance on the likelihood of humans sharing this galaxy with extraordinary 'alien' neighbours from outer space. If it all sounds too fanciful, tighten your seat-belt because we are in for quite a ride, and it may involve considerable long distance travel.