In order to commemorate the tercentenary of the death of the mathematician Pierre Varignon on 23 December 1722, we wanted to assess what we know about this savant, his scientific contributions, his personal and professional engagements, and his institutional roles. A renowned geometer in his own time, a prominent member of the Académie royale des sciences and a pivotal figure in a network of transnational correspondence, Varignon was also the inaugural mathematics professor at the Collège Mazarin and a royal reader. His combined activities of research, teaching and mediation make him one of the early 'professional' scholars at the dawn of the Enlightenment. The introduction to the book, which is dedicated to him, aims to present the themes developed in these pages, the issues tackled and the advances they enabled.