This volume of the Opera omnia will be devoted to the letters Euler exchanged in French with his friend and countryman Johann Kaspar Wettstein as well as with some Swiss scholars in and around Geneva (Louis Bertrand, Charles Bonnet, Marc-Michel Bousquet, Jean Castillon, Gabriel Cramer, Philibert Cramer, Gaspard Cuentz, Georges-Louis Lesage). It will also include a letter from Johann Michael von Loen, a remote relative of Euler mentioned in the Euler-Bertrand correspondence. Many letters published in this volume provide new information about Euler's non-scientific activities, like the commerce of almanachs, the preparation of his writings for publication, the support of young scientists in search of a position, and his insatiable need for Virginia tobacco