This article analyses the exchange of artworks between Gustave Fayet (1865-1925), a central artist and collector of the early 20th century, and Parisian art dealers. Based on unpublished archives, this work paints a portrait of a singular collection of modern art, mainly due to the multiple exchanges that allowed Fayet to gather more than 800 pieces by major artists and several masterpieces. From Impressionism to Fauvism, via Post Impressionism and Symbolism, the artworks collected by Fayet correspond not only to his artistic inclinations, but also to the laws of supply and demand. This collection, a true testimony to the tastes of art lovers in France, also reflects the evolution and fluctuations of the modern art market at the beginning of the century.