Louis Couturat (1868–1914) was a French philosopher and mathematician1. He mainly wrote works on the philosophy of mathematics and the international auxiliary language project. He was involved in the beginnings of the Revue de Métaphysique et de Morale and the founding of the French Society of Philosophy. He is known for his polemic with Henri Poincare on the "logistic" question. His extensive correspondence (1897–1913) with Bertrand Russell, published in 2001 (Russell, 2001), contains exchanges on their respective interpretations of Leibniz. We will be making use of this still relatively unexploited document in the course of this paper.