The genus Crinivirus is in the family Closteroviridae. The type member of this new genus is Lettuce infectious yellows virus (LIYV). Criniviruses have particle lengths that are roughly half the lengths reported for closteroviruses [4]. All viruses that have been assigned to the genus Crinivirus are transmitted by whiteflies, as opposed to aphids for members of the genus Closterovirus. The incidence and impact of viruses belonging to the genus Crinivirus are dependent on the interactions among several factors, including the virus itself, the host range of that virus, the specific whitefly vector(s), surrounding crops and weeds, and climatic conditions. Criniviruses are unique in that they are transmitted by one or more of the following whitefly species: B. tabaci biotype A (sweet potato whitefly, SPWF), B. tabaci biotype B (silverleaf whitefly, SLWF), Trialeurodes vaporariorum Westwood (greenhouse whitefly, GHWF), and Trialeurodes abutilonea Haldeman (banded wing whitefly BWWF). A unique characteristic of criniviruses is that some members can be transmitted by more than one whitefly vector species or biotype with different levels of efficiency. This chapter addresses criniviruses and their whitefly vectors, particularly the effect of transmission characteristics on their disease epidemiology. Knowledge of the vectors is crucial to the management of the diseases caused by these viruses.