Considering the 'One Health' principles, the links between animal and human health are very strong. Both domestic and wild animals are sources of infectious agents that cause diseases in humans. Poor animal health may also indirectly affect human health, through reduced access to food. A large number of infectious diseases of animals, the transboundary animal diseases, spread rapidly across borders. Robust and accurate diagnostic assays are needed to detect the infectious agents rapidly and to limit their spread. A large arsenal of novel assays has been developed during the last three decades, with a tremendous impact on the detection of infectious agents. The new diagnostic methods are mostly laboratory-based and expensive, requiring sophisticated equipment and special skills. However, rapid and cheap field-based assays have also been developed. Herein, the authors give several examples of the development of novel assays, with special focus on the 'One Health' principles.