Ancient astronauts refer to a pseudoscientific set of beliefs that hold that intelligent extraterrestrial beings visited Earth and made contact with humans in antiquity and prehistoric times. Proponents suggest that this contact influenced the development of modern cultures, technologies, religions, and human biology. A common position is that deities from most, if not all, religions are extraterrestrial in origin, and that advanced technologies brought to Earth by ancient astronauts were interpreted as evidence of divine status by early humans.

Pseudoscience consists of statements, beliefs, or practices that claim to be both scientific and factual but are incompatible with the scientific method. Pseudoscience is often characterized by contradictory, exaggerated or unfalsifiable claims; reliance on confirmation bias rather than rigorous attempts at refutation; lack of openness to evaluation by other experts; absence of systematic practices when developing hypotheses; and continued adherence long after the pseudoscientific hypotheses have been experimentally discredited. It is not the same as junk science.