This book summarizes the experience of many years of teamwork with my group, the beam diagnostics group of GSI. For a long time the group was also responsible for operating the machines and application programming. In my opinion, this connection was very e?cient: ?rst, because a beam diagnostic system has to place powerful tools at the operators¿ disposal; second, because data evaluation and presentation of results for machine operation demand application programs which can be handled not only by skilled experts. On the other hand, accelerator developments and improvements as well as commissioning of new machines by specialists require more complex measu- ments than those for routine machine operation. A modern beam diagnostic system, including the software tools, has to cover these demands, too. Therefore, this book should motivate physicists, constructors, electronic engineers, and computer experts to work together during the design and daily use of a beam diagnostic system. This book aims to give them ideas and tools for their work. I would not have been able to write this book without a good education in physics and many discussions with competent leaders, mentors, and c- leagues. After working about 40 years in teams on accelerators, there are so many people I have to thank that it is impossible to mention them all by name here.