This document specifies the principles of ultrasonic through-transmission techniques. Through-transmission techniques can be used for: — detection of imperfections; — determination of sound attenuation. The general principles required for the use of ultrasonic testing of industrial products are described in ISO 16810. The through-transmission technique is used for the testing of flat products, e.g. plates and sheets. Further, it can be used for tests, e.g.: — where the shape, dimensions or orientation of possible imperfections are unfavourable for direct reflection; — of materials with high sound attenuation; — on thin test objects.