This standard work provides all physicians with confidence regarding execution and evaluation of endocrinological function tests. It supports efficient diagnostics, yields valuable results, and ensures reliable assessments in endocrinology, diabetology, gynecology, urology, andrology, pediatrics, internal medicine. The content is aligned with the recommendations of national and international professional societies. This book comprises more than 200 hormonal parameters, function tests as well as validated scoring and grading systems. Basic knowledge regarding diagnostic methods in radiological and nuclear medicine as well as genotype-phenotype correlations are summarized. All parameters are rigorously correlated to age, gender, BMI, phase of life, menstrual cycle, and medication by presenting 174 tables and 66 figures. Detailed and practice-relevant, you will receive a quick overview of indications, contraindications, side effects, test preparation, framework conditions, specific action guidelines for test execution, secure evaluation of results with detailed cut off values, as well as practical tips and potential pitfalls. The 5th edition has been completely updated and expanded to include topics such as "troubleshooting" in immunoassays, paraneoplastic syndromes, screening for malnutrition, basal and stimulated copeptin, metyrapone test, macimorelin test, and digital diabetes parameters (CGM). The translation was done with the help of artificial intelligence. A subsequent human revision was done primarily in terms of content. This book is a translation of an original German edition. The translation was done with the help of artificial intelligence (machine translation by the service DeepL.com). A subsequent human revision was done primarily in terms of content, so that the book will read stylistically differently from a conventional translation.