The concept of life in the universe represents a number of ideas that have long stoked the fires of human imagination. These ideas include life on Earth traveling out into the universe, humans living elsewhere in the the universe, and extraterrestrial life and our search for it.

Although people have pondered these ideas since time immemorial, it has only been recently—within a human lifetime—that humanity has made significant strides in these endeavors. Since the 1950s, we have sent rockets and satellites into space. Since the 1960s, we have sent humans into space and returned them safely to Earth. Since the 1970s, we have sent humans to live in space for weeks, months, and even years at a time. Since the 1980s, scientifically significant searches for extraterrestrial life have been made. And since the 1990s, astronomers have discovered hundreds—perhaps even thousands—of planets orbiting stars other than the Sun.