This is the first book that comprehensively addresses the application of helium testing. It is not only a collection of recipes for those who want to carry out this sensitive and reliable testing method themselves; it also imparts the necessary expertise to incorporate such procedures into their own testing and acceptance regulations and to be a competent partner in discussions with providers of He tests and leak detectors. There is a brief but concise introduction to the fundamentals of this branch of non-destructive materials testing. The methods of leak detection and tightness testing with the helium detector are presented in detail, including their limitations and potential measurement errors. It assists in the selection of suitable equipment. It is written from practice for practice.