This Brief provides the current state-of-the-art on all key topics involved in GMO testing and is a source of detailed practical information for laboratories. Special focus is given to qualitative and quantitative real-time PCR analysis relevant to all areas where detection and identification rely on nucleic acid-based methods. The following topics, important for testing laboratories, are also discussed, organization of the laboratory, focusing on aspects of the quality system and methods for testing, validation and verification of methods, and measurement uncertainty. The Brief also discusses the new challenges of GMOs and novel modified organisms, using new technologies, and the possible solutions for GMO detection, including bioinformatics tools. Finally, legislation on GMOs and sources of information on GMOs are provided, which are relevant not only to testing laboratories, but to anyone interested in GMOs.