外星人相關的傳說一向是人們津津樂道的故事，電影《ET》更是至今永垂不朽的經典。俄羅斯的一個小鎮曾發現一個真實案例，一具外星人外型的屍體被發現，至今仍是當地廣為人知的故事，不過該生物的真實身份，目前仍眾說紛紜。
外星人（英語：Extraterrestrial intelligence，簡稱ET），舊稱宇宙人，是人類對地球以外的智慧生命的統稱。從古至今，人類對其他行星是否存在外星人，以及外星人及其文明是什麼樣的，一直存在猜測、想像、研究與探索。一些人將地球上難以用科學解釋的文明產物，或不明飛行物，都歸責於外星人及其影響。但現今人類還無法實際探查是否有外星人，甚至是外星生命的存在。
有些學術單位（其中較著名的包括哈佛大學、派崔克萊加州大學和非營利組織SETI協會等）參與了搜尋地外文明計劃（SETI）。這些組織致力於用無線電望遠鏡等先進設備接收從宇宙中傳來的電磁波，從中分析有規律的信號，希望藉此發現外星文明。
Extraterrestrial intelligence (ET), formerly known as the cosmic person, is the collective name of human beings for intelligent life outside the earth. From ancient times to the present, human beings have been speculating, imagining, researching and exploring whether aliens exist in other planets, as well as aliens and their civilizations. Some people attribute the products of civilization, or UFOs, that are difficult to explain scientifically on Earth to aliens and their influence. But nowadays humans can't actually detect whether there are aliens or even alien life.
Some academic units, including the more famous ones including Harvard University, the California University of Patrick and the non-profit organization SETI, are involved in the Search for Extraterrestrial Civilization Program (SETI). These organizations are committed to receiving electromagnetic waves from the universe using advanced equipment such as radio telescopes, and analyzing regular signals from them, hoping to discover alien civilizations.
