When the first edition of this book was published more than a decade ago, validation was a challenge for many laboratory managers. Now, advancements in methods and the demands for reliability and transferability of measurement results have established validation as an integral part. This raises questions for laboratory management and quality assurance, such as: What must absolutely be validated, and what is the significance of validation data? What is mandated by whom, and where do we have freedom? How can we validate quickly and cost-effectively, yet correctly? The answers can be found even more effectively with the second edition of this manual. Proven elements have been retained, such as the pedagogically valuable structure, numerous examples and tables, and the significantly expanded glossary. The chapters on validation in spectroscopy have been thoroughly revised and expanded.