Nuclear physics has undergone stupendous developments since its beginnings approximately a century ago. The field developed into particle and high-energy physics, culminating in the discovery of the Higgs boson at the Large Hadron Collider at CERN in 2012. The study of nuclear reactions not only tells us about the nature of the forces that act within nuclei, but studying such reactions provides a basic tool used to elucidate the structure of nuclides. In this book the author charts the developments in nuclear reaction physics since its inception by reviewing the crucial experiments that helped drive and shape our understanding of the field. It is fascinating to look at theoretical developments in the area of subatomic physics in step with the grand new ideas of the early 20th century where quantum theory and the theory of relativity opened up entirely new views of the world. Experiments had to provide answers to alternative theoretical interpretations, but also gave hints as to "new physics" and challenges to the contemporary perception of the nuclear and sub-atomic worlds. In this respect, it is enlightening to study the details of early experiments, where quite often epoch-making results were obtained with very simple means, but all those experiments were based on earlier attempts that were carefully refined to yield unambiguous evidence. Here the crucial experiments that often, but not always have been the first in a subfield, are described in some detail, often including original drawings or detailed experimental setups. A look back in time to the beginnings and key discoveries will help better understand how the often very sophisticated and complex experiments of today came about. For readers interested in questions of the history of science it is also instructive to learn how misinterpretations and prejudices prevented or delayed early fundamental breakthroughs.