Growing awareness of the gap in coordination and resources for plant disease diagnostic assay development and validation inspired Kitty Cardwell Director of the Institute for Biosecurity and Microbial Forensics at Oklahoma State University and colleagues, in collaboration with The American Phytopathological Society (APS), to publish the focus issue “Diagnostic Assay Development and Validation: The Science of Getting It Right” in the journal PhytoFrontiers. This visionary and widely collaborative focus issue contains more than twenty-five open access articles addressing the need to harmonize plant health diagnostics within the United States agricultural biosecurity system.