About 13 million pages of declassified documents from the US Central Intelligence Agency (CIA) have been released online.
The records include UFO sightings and psychic experiments from the Stargate programme, which has long been of interest to conspiracy theorists.
The move came after lengthy efforts from freedom of information advocates and a lawsuit against the CIA.
The full archive is made up of almost 800,000 files.
They had previously only been accessible at the National Archives in Maryland.