Such considerations have led to the popular view that these things must come from some more highly advanced extraterrestrial civilisation.

This has resulted in the elimination of entire extraterrestrial civilizations on numerous worlds.

They're a group of whackos who want to find extraterrestrial civilizations.

The question of extraterrestrial civilizations seems to me entirely open.

After establishing contact with extraterrestrial civilizations, it was found that humans were the only race to develop various sports.

Why isn't there evidence of extraterrestrial civilization all around us?

We may have wildly overestimated the abundance of extraterrestrial civilizations.

There are two ways that astronomy might find evidence of an extraterrestrial civilization.

There is considerable speculation why a extraterrestrial civilization might exist but choose not to communicate.

All discussions of extraterrestrial civilizations therefore have to be purely speculative.