This book gives a detailed account of the most interesting period in the life of the Dutch humanist scholar Isaac Vossius (Leiden 1618 – Windsor 1689). It is largely based on Vossius’s extensive correspondence, much of which has never been published before. In particular, Isaac’s correspondence with his father, Gerardus Joannes Vossius, has been thoroughly investigated and is a prime source of information here. Isaac Vossius’s travels through England, France and Italy followed his formative years at Leiden and Amsterdam, during which time he had come under the strong influence of the French scholar, Claude Saumaise. A narrative account of these travels is given, and Vossius’s contacts with the various circles of scholars that he encountered are discussed in detail. Such contacts allowed him to enter libraries otherwise difficult of access, and there he continued his search for manuscripts. Vossius’s period as a wandering scholar can be said to have been rounded off with the year that he spent in Paris, as secretary to Hugo Grotius. All this time Vossius was building up his own collection of books, and the fruits of these library researches were the philological editions that he began to publish in the four years that followed. A new phase of Vossius’s life opened in 1648, when Queen Christina of Sweden invited him (then still only thirty) to come to her court. The following six years were the most turbulent in the scholar’s life. He became the queen’s tutor in Greek, and also her personal confidant. Under Vossius’s guidance, the queen steeped herself in the study of Plato and the Neoplatonists; while the philosophy of Descartes – whom she likewise invited to Stockholm – seems to have held little interest for her. It was while Vossius was at the Swedish court that he finally came into open conflict with Saumaise, his former mentor. Vossius built up a magnificent library for Christina. This collection was however dispersed even before it has been completed; though, unfortunately, not before Vossius’s own books had been inadvertently incorporated into that library. With the queen’s approval, Vossius then selected a new collection for himself from the royal library. In 1655 Vossius, disillusioned, withdrew to the quiet of his own study, in The Hague. Since 1690 his collection of books and manuscripts has been housed in the University Library at Leiden, where it forms the basis of the international fame of that institution.