(clarify numbers in Incunabula Catalog)
The [[Gutenberg Bible]] was printed as a folio in about 1455, in which four pages of text were printed on each sheet of paper, which were then folded once. Several such folded conjugate pairs of leaves were inserted inside another to produce the sections or gatherings, which were then sewn together to form the final book.
The oldest surviving octavo book apparently is the so-called "Turkish calendar" for 1455, presumably printed in late 1454, about the same time as the Gutenberg Bible. <ref> [http://istc.bl.uk/search/search.html?operation=record&rsid=356&q=0 British Library, Incunabula Short Title Catalogue, entry for the 1454 Turkish Calendar]. </ref> <ref> Margaret Bingham Stillwell, ''The Beginning of the World of Books, 1450-1470, [[Bibliographical Society of America]], New York, 1972, p. 6, described as a tract of 6 leaves, but not identifying the format. </ref> Numerous other octavos survive beginning from about 1461. <ref> [http://istc.bl.uk/search/search.html?operation=search&rsid=356&sort=idx-year British Library, Incunabula Short Title Catalogue search for octavos, sorted by year] </ref>
Beginning in 1501, [[Aldus Manutius]] of Venice began to print classical works in small octavo format which were easily portable. These editions contained only the text of the works, without the commentary and notes, and became extremely popular with educated readers. As a result, Aldus became closely associated with the octavo format. <ref> Martin Lowry, ''The World of Aldus Manutius,'' [[Cornell University Press]], 1979, pp. 137-167. </ref>