Index Librorum Prohibitorum
The Index Librorum Prohibitorum (Index of Prohibited Books) is a list of publications which Roman Catholics were banned from reading, "pernicious books", and also the rules of the Church relating to books. The aim of the list was to prevent the reading of immoral books or works containing theological errors and so prevent the corruption of the faithful. The index was ended in 1966 under Pope Paul VI.
Created in 1559 by the Sacred Congregation of the Inquisition of the Roman Catholic Church (later the Congregation for the Doctrine of the Faith). The index was regularly updated until the 20th edition of 1948 with materials being added by either the Congregation or the Pope. The list was not simply a reactive work; the authors were encouraged to defend their works, they could re-publish with elisions if they wished to avoid a ban, and pre-publication censorship was encouraged.
It had great effect throughout much of the catholic world. For many years in areas as diverse as Quebec and Poland it was very difficult to find copies of indexed works, especially outside of major cities.