The Harz is the most geologically diverse and complex low mountain range in Germany and at the same time a popular tourist destination. It is characterized by shale, graywacke, flysch, and granite plutons of Variscan age. The authors, who have spent many years teaching and researching the Harz, provide a concise introduction to the geology of the Harz and explain its formation. A brief yet modern overview of the geology of the Eastern Harz and the crystalline of the Kyffhäuser is presented. Specific rocks and structures are introduced in the excursion section of the guide, featuring attractive, easily accessible outcrops in the Eastern Harz and Kyffhäuser. These are summarized into 11 spatially limited excursion routes that can be explored by car, on foot, or by bicycle. Some excursions include Kyffhäuser, Bodetal, and Wan.