Researchers and students have not yet had access to a book which would enable them to trace the origins of the concepts that explain the behavior of materials under irradiation. This book fills the gap. As far back as antiquity, the notions of purity and disorder have been evoked to explain the different properties of materials. It was geologists who developed the subject in the 19th century. Then, with the discovery of X-rays and radioactivity, disorder in materials became the domain of physicists and chemists. The first observations focused on the color changes of ionic crystals, then gradually all the techniques for characterising materials were used. However, questions about the resistance of the components of the first atomic piles to irradiation led to the development of irradiation studies. This book describes the historical approaches to particle transport and defect creation mechanisms. Several chapters detail the history of irradiation of different types of materials: metals, semiconductors, iono-covalent insulators, polymers and radiolysis of water. The final two chapters deal with irradiation tools and applications.