Before the establishment of the Alfaflexiviridae and Betaflexiviridae families, these viruses were classified under the now-defunct Flexiviridae family within the Riboviria realm. The International Committee on Taxonomy of Viruses (ICTV) officially recognized these two new families in 2004. This reclassification aimed to organize several existing genera and previously unassigned species of plant-infecting viruses. The names of these families highlight the characteristic flexuous and filamentous morphology of their virions, distinguishing them from other plant virus families, such as Closteroviridae and Potyviridae (Table 15.1). Notably, viruses within the Alphaflexiviridae family lack a protease domain, exhibiting a unique lineage of replication proteins akin to those found in alphaviruses. These viruses demonstrate a broad host range, infecting both herbaceous and woody plant species.