Charles Messier corresponds with French and foreign astronomers and academicians. He becomes a member of the Royal Society of London, of the Academies at Berlin and Saint Petersburg, of the French Académie des Sciences, and, ultimately, of several Academies in Sweden, Netherlands and at Bologna.

The following letters are addressed to :

-        Jean-Dominique Maraldi (1709-1788), a member of the French Académie des Sciences and Cassini III's cousin

-        Etienne-Hyacinthe de Ratte (1722-1805), a member of the Academy at Montpellier

-        Pierre-Charles Le Monnier (1715-1799), a member of the French Académie des Sciences and a professor at the Collège de France

-        Honoré Flaugergues (1755-1830), a justice of the peace at Viviers, an astronomer and archaeologist, and Etienne-Hyacinthe de Ratte's nephew