To question the fanaticism of the truth that governs philosophy, to recognize life alone as the source of all value, independence for the supreme virtue of the philosopher, and to seek an unprecedented reconciliation of art and science: this is the meaning of gay knowledge for Nietzsche. Published in 1882, this book is republished and expanded in 1887.It implements the main themes of Nietzsche's thinking, including that of eternal return, which he introduces here for the first time. The author unfolds the project of a healing of humanity, of a renewed strength and love of life: "the supreme hope" which can be conquered only in pain... and in drunkenness.