Get ready to embark on the exciting search for dark matter-the invisible mass that dominates our universe. This popular science book explains why this mysterious dark matter has been incorporated into the standard model of the universe and how scientists are able to "observe" the invisible. The book starts with the early indications of the existence of dark matter, including the strange cohesion of galaxy clusters, before moving on to modern observations like cosmic background radiation. Along the way, you will learn about the direct and indirect methods being used by researchers to track down dark matter and whatever is behind this strange phenomenon. This book will appeal to general readers who wish to understand what scientists actually know about dark matter, along with the methods they use to help crack the mystery. The book is a translation of the original German with the help of artificial intelligence (machine translation by the service DeepL.com). A subsequent human revision was done primarily in terms of content, so that the book will read stylistically differently from a conventional translation. Springer Nature works continuously to further the development of tools for the production of books and on the related technologies to support the authors.