Finally, decades after the United States Air Force closed their official investigations into the UFO phenomenon, the files are online in their entirety for free.
Project Blue Book is regarded as the third UFO investigation project by the USAF. The first was Project Sign, which began in 1947, then Grudge, which ran from 1949 to 1951, and the final project, Blue Book, ran from 1951 to 1969. The files surrounding the investigation of the sightings are all included in the Project Blue Book files. That is, unless, as some suggest, there are secret investigations that the public still does not have access to.
Either way, although these files have all been declassified, since the close of Project Blue Book, it has taken a trip to the National Archives to get full access to them. Some websites have put up portions of the files, and one website, Fold3, finally posted all of them a few years ago. However, visitors could just view them and had to pay a membership fee to download them.
Note: Apparently you can download the files at Fold3 for free now, but it is one page at a time, and in the jpeg picture format. The Black Vault offers the files in PDF documents, making it much quicker and easier to download. Many of them are also searchable.
Now researchers and UFO enthusiasts, including myself, can save some money. The files have been placed online by John Greenewald who runs a website called The Black Vault. Greenewald has been submitting Freedom of Information Act (FOIA) requests since he was a teenager to get the government to share what it knows about UFOs and other clandestine matters.
He has posted these files online, and over the years has amassed the largest online repository of such materials. He has over one million pages hosted there. Now that he has finally finished the daunting task of making the Blue Book files available, he now has over 130,000 more.