In this guideline the methods of testing vacuum coated plastic parts that have become established practice for manufacturers and users will be presented. As a rule, one must always verify whether the selected procedure really addresses the characteristics that will be relevant under the actual conditions of use and whether they can be tested in a reproducible manner. The testing of decorative, anti-friction, antiabrasion, electrical, optical and other functional coatings will be presented in detail. A differentiation will be made between testing for the approval of an entire series and the routine testing conducted during serial production. The many testing and examination procedures used for research and development purposes will not be considered, since these, often highly complex procedures, are only seldom used in everyday coating practice. They are, however, of great importance in making assessments in the event of damage and for discovering the causes of defects.