This paper examines how Henry Oldenburg became a man of scientific communication during the years 1656-1663. His interest in the new natural philosophy started in the mid-1650s when, while visiting England, he became acquainted with men like Robert Boyle and Samuel Hartlib. Embarking on a trip over Europe as tutor to Richard Jones, Boyle's nephew, he also began to practice merchandising in knowledge. His communication skills quickly developed, for he learned a great deal from his personal contacts with men of science and from his correspondence with Hartlib, Boyle, and others. His prolonged stay in Paris in the late 1650s was very important for there he acquired an experience of the intellectual life of the private scientific academies, and gained for himself a host of new correspondents. The paper concludes by looking at Oldenburg in his role as mediator in the Spinoza-Boyle debate of 1663. By that time, at the beginning of his career as Secretary of the Royal Society, he was already a well-rounded ‘philosophicall merchant’.