From the FDsys site:
“The Public Papers of the Presidents, which is [sic] compiled and published by the Office of the Federal Register, National Archives and Records Administration, began in 1957 in response to a recommendation of the National Historical Publications Commission. Noting the lack of uniform compilations of messages and papers of the Presidents before this time, the Commission recommended the establishment of an official series in which Presidential writings, addresses, and remarks of a public nature could be made available.”
At present, the papers of Presidents Clinton, Bush père et fils, and Obama are freely available here.
Ernster, the Virtual Library Cat