Miscellaneous manuscripts, i. e. manuscripts containing texts by various authors, are the products of a long process which reversed a fundamental law of the ancient 'book industry' whereby books were conceived to contain a single author's texts. Why did this new type of book appear? What was its impact in the book industry of the Middle Ages? What were the goals of the copyists who produced such manuscripts? The book attempts to answer these questions by examining fourteen Byzantine manuscripts from the IXth-XIIth centuries preserved in major European libraries (e.g. Biblioteca Apostolica Vaticana, Oxford Bodleian Library, Heidelberg Universitätsbibliothek, Leiden Bibliotheek der Rijksuniversiteit, Archivio e Biblioteca dell'Abbazia of Montecassino, Munchen Bayerische Staatsbibliothek, Bibliothèque nationale de France in Paris, Venice Biblioteca Nazionale Marciana). By the variety of their contents and level of production, these manuscripts are representative of the totality of manuscripts produced in the Middle-Byzantine period. However, the perspective of the investigation is a wider : each manuscript is analysed following a new method of studying palaeographic, codicological and philological features all together. Such a method reveals not only the cultural level of the copyst and his way of working, but also the interests and the economic conditions of the commissioners. Finally, an extensive section devoted to methodology focuses on typological problems, reviewing the most ancient miscellaneous manuscripts (on papyrus rolls), as well as Latin miscellanei and miscellaneous incunabula and cinquecentine.