Since the invention of writing, there has always been a need to conceal written content from unauthorized readers. The study of secret writing is therefore almost as old as writing itself. However, as a science in the modern sense, cryptography is still very young. The method of visual cryptography invented by Naor and Shamir in 1994 distributes an image across two sheets in such a way that each individual sheet only displays a random pattern of dots, but when both sheets are overlaid, they reveal the secret image. This book provides insight into this current field of research, deliberately avoiding so-called higher mathematics. It is therefore ideal as a foundation for proseminars and math clubs at the secondary level. Exercises with sample solutions help to deepen the understanding of the material.