First edition. Gaston Julia (1893-1978), a member of the Institute and professor at the École Polytechnique, was a leading French mathematician, famous for his work on fractals (Julia set). His Cours de Géométrie (Course in Geometry) is a textbook derived from his teaching at the École Polytechnique, a prestigious institution that trains France's scientific and technical elite. This work reflects the methods and content of geometry teaching in the mid-20th century, a field that remains fundamental despite the emergence of new branches of mathematics. Julia's course was renowned for its clarity and rigor.