By 1812 we find a completely modern conception of bibliography. Gabriel Peignot cites no bibliographer from classical times and names only such older writers of the Renaissance as have not been superseded by more recent authorities. This definition of the bibliography of bibliographies makes it practically useful to the writer's contemporaries. With the exception of Theodore Besterman, the subsequent writers of bibliographies of bibliographies have been practical men who see a modern librarian's needs and more especially, when that functionary is invented, the needs of a reference librarian. Julius Petzholdt admits many old bibliographies to his _Bibliotheca bibliographica_ of 1866, but gives them room only for historical reasons or in the absence of a modern work. Joseph Sabin goes somewhat farther by restricting himself to British and American bibliographies with only a side glance at those in other than European languages. Léon Vallée, Henri Stein, W. P. Courtney, and those who come after show a more and more definitely acknowledged restriction to modern works and especially those within the easy reach of their readers. The bibliography of bibliographies becomes an ever more skilfully fashioned key to unlock modern learning and modern libraries. In the last two generations cooperative effort has become characteristic of much bibliographical work and the publication of periodical surveys limited to brief periods and cumulated for longer intervals reflect both the difficulty of the task and the emphasis on contemporary usefulness. The standards of accuracy and, within the limits that have been accepted, the standards of completeness have enormously improved.