As all bibliographers have at one time or another, Labbé included some titles that had little to do with his task. The differentiation of biography and bibliography was perhaps less clear then than now, and general treatises on scholarly matters probably seemed more closely akin to bibliographies than we find them to be. Honoratus Montecalvus, _Speculum tragicum Regum, Principum & Magnatum superioris seculi celebriorum ruinas exitusque calamitosos breviter complectens_, which is adequately described by its long title, is not a bibliography but one of many accounts of the mishaps that have befallen great men. Jacobus Gretser, _De jure et more prohibendi, expurgandi et abolendi libros haereticos et noxios_ is obviously a book about books, but it is scarcely a bibliography. Although Jacobus Middendorpius's famous treatise on universities is a general account of its subject, Labbé is probably too generous in admitting it. These examples suggest some laxity in Labbé's definition of bibliography. In its conception and execution the _Bibliotheca bibliothecarum_ is excellent. Although rarely consulted, it is still valuable for reference purposes. An occasional difficulty will arise, but a modern reader must not object to Labbé's short titles.[69] _Theatri_, which was then immediately understood as a citation of Theodor Zwinger, the Elder (ed.), _Theatrum vitae humanae_, a standard sixteenth-century encyclopedia, was then no more difficult to understand than _The New International_ might be today.[70] Labbé is a good bibliographer because he cites pertinent references to non-bibliographical books.[71] He is careful to indicate whether he has seen the book he is citing[72] and occasionally comments on its bibliographical value.[73] In brief, Labbé's _Bibliotheca bibliothecarum_ is well conceived, neatly arranged, and relatively accurate in details. In plan and arrangement it surpasses, for example, such a modern work of similar size and purpose as _A Bibliography of Bibliographies_ that the famous bibliographer Joseph Sabin published in 1877. As I have already said, the references are as accurate as those to be found in three of the bibliographies of bibliographies published in the last seventy years. His choice of an arrangement according to authors' names has been adopted only by Joseph Sabin (1877) and Léon Vallée (1883-1887). Unpopular as it has been, it nevertheless seems to me a good method of dealing with intractable material. A classified bibliography requires both an index of subjects and an index of authors. An alphabetical index of subjects requires cross-references and an index of authors. Labbé's _Bibliotheca bibliothecarum_ needs only a new index of subjects to become a reference work useful to a modern scholar.