Each epoch in the history of bibliographies of bibliographies has an individuality of its own. In the hands of Conrad Gesner and his successors this variety of bibliography slowly established itself. In the next epoch the work of Philip Labbé attracted contemporary scholars to continue and improve it. Although Antoine Teissier was the only one to publish the revision of a predecessor's work, his procedure is characteristic of seventeenth-century scholarship. The eighteenth century neglected the bibliography of bibliographies and let the writings of the sixteenth and seventeenth century in this field sink into obscurity. In the nineteenth century, as we shall see, men undertook to compile bibliographies of bibliographies with an astonishing disregard of the difficulties of the task and a surprising neglect of previous efforts. Without an exception these men were librarians and should therefore have been fully aware of what they were doing and of what had been done. Their behavior is nothing less than amazing. I may anticipate the theme of the next chapter by saying that the characteristic aspect of the making of bibliographies of bibliographies in the twentieth century is cooperation. When the great French bibliographer Gabriel Peignot (1767-1849) published his _Répertoire bibliographique générale_ in 1812, he declared that he had hit upon an entirely new idea. Although he knew and cited such predecessors as Labbé and Teissier, he did not clearly see that he was undertaking the task that they had already completed. He did not use their books systematically, and he did not exhaust the information that they had collected.