In these volumes, I have undertaken to present a record of the Indexes which have been issued under the authority of the Church of Rome, or which, having been compiled by ecclesiastics, were published under the authority of the State, between the year 1546 (the date of the first list of prohibited books which may properly be described as an Index) and 1900, in which year was issued the second Index of Leo XIII, the latest in the papal series. To this record I have added a selection of the more noteworthy examples of censorship during the earlier centuries of the Church (a list which begins with a curious prohibition in 150, probably the earliest instance of censorship by a Church council); a schedule of the more important of the decrees, edicts, pastoral briefs, etc., issued under ecclesiastical authority, which had to do with the matter of censorship; and a specification of certain censorship regulations which, before the publication of the first Index, came into force in the several States of Europe. Such a schedule of decrees and regulations can, of course, lay no claim to completeness. I have attempted simply to present examples of prohibitions and condemnations, from decade to decade, which were typical or characteristic, and from which some impression could be gathered as to the nature and the extent of the censorship experiments throughout the centuries in the several communities concerned. A brief account has been added of the organisation and of the operations of the Roman Inquisition and of the Congregation of the Index, as it was from these bodies that emanated the series of papal Indexes, and with them rested, from the middle of the sixteenth century, the responsibility for the shaping of the general policy of the Church in regard to censorship. The plan of the treatise does not render it practicable to attempt any general survey of political censorship or the censorship of the State, but I have presented a brief selection of examples of State action in censorship, in order to make the necessary comparison between the methods followed by the State and those of the Church, and to make clear that the censorship of the Roman Church was (at least outside of Spain) not so autocratic in its principles, nor so exacting and burdensome in its methods, as was the censorship which was from time to time attempted by State governments acting for the most part under Protestant influence.