The correspondence of the Dutch physicist Christiaan Huygens allows us to explore the materiality of seventeenth-century scholarly exchanges. The information systems constituted by epistolary exchanges were based primarily on infrastructures that used ordinary postal services, commercial networks, and diplomatic channels. The composition of the letters reveals the close link between writing practices and the ethical requirement of precise scientific conduct. Along with the letters, drawings, books, and objects also circulated. The administration of proof presupposes the use of graphic artifices, new forms of publication (such as journals), but also instruments, as a means of conducting one’s own experiments or observations. Scientific information is not limited to the abstractions of demonstrations or reports, but is embodied in a profuse materiality that carries with it the socio-epistemic values of the scholarly community and combines the rhetorical, conversational, and polemical functions of the epistolary device.