To honour W C Roentgen and review the entire area of X-ray development in the various fields of natural, technical, and life sciences, his successors at the Physikalisches Institut of the Universitat Wurzburg organized a conference, named "Roentgen Centennial". It took place at the new "Physikalisches Institut" not far from the historical site shortly before the actual 100th anniversary of the discovery. Over forty renowned scientists were invited as representative speakers in the various subfields of X-ray activities. They reviewed the development, gave examples, and described the present status. Most of them provided survey articles, which are gathered in this book. Since most X-ray-related activities are somehow represented, an almost complete overview of the entire field is provided. This book thus represents the enormous breadth of X-ray activities and allows one to recognize the potential and quality of today's X-ray research.