Publishers of Mercurius Librarius, by their unreasonable demands for inserting the titles of Books; and also their imperfect Collecting; omitting many; and refusing all under 1sh[illing] [in] Price; hath occasioned the Printing of this Catalogue: wherein those defects are rectified. A comparison of the numbers of titles listed in the late 17th and early 18th century term catalogues and numbers the English Short Title Catalogue provides justification for these complaints. Structure and Scope The 161 catalogues printed between 1668 and 1711 show an increase in the number of titles. The average catalogue listed 109 books under 10 headings. Some catalogues had up to 13 headings; the minimum was six in the small catalogue that appeared for Hillary 1708. The first catalogues had begun with 40 to 50 titles; later catalogues reached 150 to 200 titles. The Easter catalogue of 1689 listed the exceptional number of 293 books. All catalogues opened with a Divinity section and closed with a section of books reprinted. Most of the catalogues offered additional advertisements at the end to announce ongoing projects looking for subscribers and sponsors. The sequence of categories in between varied. History was most often the second heading, Miscellanies usually the one before the Reprinted section. Other prominent headings were Physick (medicine), Mathematicks (comprising Architecture and Navigation in several of the catalogues), Poetry and Plays, Musick, Navigation, Globes, Maps, Cards, Charts, Plates (in the sense of illustrations), Law, Libri Latini (& François), Headings such as Architecture, Heraldry and Astrology remained rare. None of the catalogues offered a unified section for fiction, or for literature in the modern sense. Novels were customarily listed among the "Histories"—the majority of which were non-fictional—and sometimes as "Miscellanies". The category "Poetry and Plays" was reserved for verse and stage plays. The following table looks at all titles under the eleven most prominent headings, with a perspective on the decades and the overall trends: A comparison with modern ESTC data proves that the Term Catalogues remained highly selective. The ESTC lists between more than 13,000 and almost 23,000 titles for the individual decades. The Term Catalogue numbers range at 20%-30% of that. Catalogues of the 1690s had the greatest average numbers of titles, but ESTC data imply that the 1690s actually saw a slight drop in total title numbers. The distortions are partly the result of the project's instability in 1708 and 1709. They reflect, in part, the continuous