Reliable and rapid diagnostic methods are essential to support inspection activities conducted by National Plant Protection Organizations (NPPOs) in the framework of their official mandate, and to evaluate the efficacy of control measures taken. Since 1998 the European and Mediterranean Plant Protection Organization (EPPO) has been supporting the harmonization of diagnostic methods for regulated pests in the EPPO region through the development of technical standards. In order to increase active collaboration among the organizations involved in plant health research activities at the national and regional levels, Euphresco (European Phytosanitary Research Coordination) was established in 2006 and funded by the EU as an ERA-NET project. Euphresco has subsequently evolved into a self-sustaining international network hosted by EPPO. This paper describes the EPPO diagnostic programme. It will also provide some examples of research projects funded through Euphresco that have provided valuable support for the development of pest-specific diagnostic protocols and will show how NPPOs can shape the research agenda of research funders and help to identify gaps to be addressed through transnational collaboration.