Its secretive nature and undoubted connection to classified aircraft research, together with reports of unusual phenomena, have led Area 51 to become a focus of modern UFO and conspiracy theory. Some of the unconventional activities claimed to be underway at Area 51 include:
- The storage, examination, and reverse engineering of crashed alien spacecraft (including material supposedly recovered at Roswell), the study of their occupants (living and dead), and the manufacture of aircraft based on alien technology.
- Meetings or joint undertakings with extraterrestrials.
- The development of exotic energy weapons (for SDI applications or otherwise) or means of weather control.
- The development of time travel technology.
- Activities related to a supposed shadowy one world government.
Many of the hypotheses concern underground facilities at Groom or at nearby Papoose Lake, and include claims of a transcontinental underground railroad system, a disappearing airstrip (nicknamed the "Cheshire Airstrip", after Lewis Carroll's Cheshire cat) which briefly appears when water is sprayed onto its camouflaged asphalt, and engineering based on alien technology.