One of the methods of teaching that has brought significant contributions to the field of education is augmented reality. This technology transformed learning into a more motivating, enjoyable, fun, and interesting activity. This chapter contributes an augmented reality application for mobile devices that complements and supports the learning of geometric figures. The application, called AGeRA, consists of a geometry book and software capable of reading special markers inserted into the book's content. When this book is placed in front of the camera of a mobile device, 3D objects, sounds, animations, and other interactive elements leap from book pages making learning more fun and exciting. Preliminary tests were made with teachers and students and showed good acceptance of the application to support the teaching of geometry.