For the first time, the CIA has released online about 13 million pages of declassified documents.
The documents were uploaded following lengthy efforts from freedom of information advocates and a lawsuit against the CIA.
The records include intelligence briefings, research papers, UFO sightings and psychic experiments.
The full archive is made up of almost 800,000 files.
The release includes the papers of Henry Kissinger, who served as secretary of state under presidents Richard Nixon and Gerald Ford, as well as several hundred thousand pages of intelligence analysis and science research and development.
Among the more unusual records are documents from the so-called Stargate program, which dealt with psychic powers and extrasensory perception.
Those include records of testing on celebrity psychic Uri Geller in 1973, when he was already a well-established performer.
Memos detail how Uri Geller was able to partly replicate pictures drawn in another room with varying – but sometimes precise – accuracy, leading the researchers to write that he “demonstrated his paranormal perceptual ability in a convincing and unambiguous manner”.
Other unusual records include a collection of reports on flying saucers, and the recipes for invisible ink.
While much of the information has been technically publicly available since the mid-1990s, it has been very difficult to access.
The records were only available from four physical computers located in the back of a library at the National Archives in Maryland, between 09:00 and 16:30 each day.
A non-profit freedom of information group, MuckRock, sued the CIA to force it to upload the collection, in a process which took more than two years.
At the same time, journalist Mike Best crowd-funded more than $15,000 to visit the archives to print out and then publicly upload the records, one by one, to apply pressure to the CIA.
Mike Best wrote in a blog post: “By printing out and scanning the documents at CIA expense, I was able to begin making them freely available to the public and to give the agency a financial incentive to simply put the database online.”
In November, the CIA announced it would publish the material, and the entire declassified CREST archive is now available on the CIA Library website.
New declassified documents reveal the US National Security Agency spied on Martin Luther King and Muhammad Ali during the height of the Vietnam War protests.
The documents show the NSA also tracked journalists from the New York Times and the Washington Post and two senators.
Some NSA officials later described the programme as “disreputable if not outright illegal”, the documents show.
The operation, dubbed “Minaret”, was originally exposed in the 1970s.
However, the names of those on the phone-tapping “watch list” had been kept secret until now.
The secret papers were published after a government panel ruled in favor of researchers at George Washington University.
New declassified documents reveal the NSA spied on Martin Luther King and Muhammad Ali during the height of the Vietnam War protests
The university’s National Security Archive – a research institute that seeks to check government secrecy – described the names on the NSA’s watch-list as “eye-popping”.
The NSA eavesdropped on civil rights leaders Martin Luther King and Whitney Young as well as boxing champion Muhammad Ali, New York Times journalist Tom Wicker and Washington Post columnist Art Buchwald.
The agency also monitored the overseas phone calls of two prominent US senators – Democrat Frank Church and Republican Howard Baker.
Many of those targeted were considered to be critics of US involvement in the Vietnam War.
In 1967 the strength of the anti-war campaign led President Lyndon Johnson to ask US intelligence agencies to find out if some protests were being stoked by foreign governments.
The NSA worked with other spy agencies to draw up the “watch lists” of anti-war critics, tapping their phone calls.
The programme continued after President Richard Nixon entered the White House in 1969. US Attorney General Elliot Richardson shut down the NSA programme in 1973, just as the Nixon administration was engulfed in the Watergate scandal.
The latest revelations come as the NSA is embroiled in fresh controversy over its surveillance programmes.
US intelligence leaker Edward Snowden recently exposed far-reaching electronic surveillance of phone records and internet traffic by the agency.
Researchers Matthew Aid and William Burr, who published the documents on Wednesday, said the spying abuses during the Vietnam War era far surpassed any excesses of the current programme.
“As shocking as the recent revelations about the NSA’s domestic eavesdropping have been, there has been no evidence so far of today’s signal intelligence corps taking a step like this, to monitor the White House’s political enemies,” they wrote.