The penetrant testing of materials is a specialized method for non-destructive testing of the surfaces of metallic and non-metallic materials. The book covers the physical and process-specific fundamentals, the testing medium systems, the equipment, testing, and evaluation techniques of penetrant testing, the classification and assessment of indications, the limitations of the testing method, as well as relevant occupational and environmental protection. It thus provides the materials tester with the necessary tools for their practical work, including the most important standards and regulations to be observed.