Ahmed Hadidi is an Emeritus Lead Scientist for the U.S. Department of Agriculture, Agricultural Research Service, Beltsville, Maryland, USA. He obtained his BS Summa Cum Laude from Cairo University in 1958, MS from the University of Minnesota in 1962, and PhD from Kansas State University in 1967. In 1973, at the Department of Molecular Biology and Virus Laboratory, University of California, Berkeley, he was the first to characterize and study the specificity of the soluble RNA-dependent RNA polymerase (RdRp), known as replicase, of a eukaryotic RNA virus, which is specific to the infected tissue. RdRp is indispensable for replicating the viral RNA genome as well as for carrying out transcription. He joined the U.S. Department of Agriculture, Agricultural Research Service, and Plant Virology Laboratory in 1975. His research interests have included molecular virology, molecular biology, genetic engineering, and genomics. Moreover, he is the Senior Editor of four textbooks on plant viruses and viroids published in 1998, 2003, 2011, and 2017. He has served as a Member of the Editorial Board of several virology and plant pathology journals, including having served as the Senior Editor (Virology) of the Journal of Plant Pathology.