The geometry of circles is ideally suited to unlock the richness of geometry. Starting from the classical theorems of circle geometry that are over 2000 years old, the author extends the discussion to modern times, where new tools of circle geometry, primarily developed by Jacob Steiner, provided a tremendous boost. This allows him to address a wide range of topics that includes not only many famous theorems but also numerous lesser-known results. To make the proof ideas and their geometric core transparent, the geometric reasoning is emphasized in all proofs. Over 250 illustrations and a relaxed yet precise writing style accompany the reader on this fascinating journey through circle geometry.