The recent discovery of the marquis de Mirabeau’s lifelong correspondence with his Swiss friend Frédéric de Sacconay has shed new light on the development of his economic thought. Not only is it the only precise entry in his daily life leading to his fame, but it also clarifies the context in which important eighteenth-century texts have been produced and read. Amongst this collection of letters, one of them, written by Mirabeau on October 12, 1740, establishes that he possessed a manuscript of Cantillon’s Essai sur la nature du commerce en général at the time. This fact renews the insight on his intellectual origins and on the genesis of the Ami des hommes. Indeed, conceived at first as a commentary of the Essai, Mirabeau’s most famous work is the result of a project that dates back to his youth. Already concerned about France’s decline, the future physiocrat wrote to his Swiss friend to express his nascent thoughts on agricultural sciences and commerce, thus giving his first economic statement known to date.