This book is intended for first-year university students. It presents the course of geometrical optics in a simplified and pedagogical way. Structured in 5 chapters, it deals with the essentials of geometrical optics: the principles, the foundations and the basic laws for the study of planar systems (plane mirror, blades with parallel faces...), spherical diopters and thin lenses. Demonstrations and images are provided to help the student assimilate the content of various notions and relationships.