Yellow fever virus (YFV) is an arboviral flavivirus (enveloped, positive-sense single-stranded RNA), and is considered the “prototype” flavivirus. There is one serotype of YFV divided into three genotypes: I, IIA, and IIB. YFV is maintained in non-human primate reservoirs and is transmitted by mosquitoes via urban and sylvatic cycles. YFV is zoonotic and has been recognised in Central and South America as a significant cause of disease in humans since the 1600s. This technical card focuses on disease in nonhuman primates unless specifically stated.