This chapter provides a brief account of the development of studies on structure, composition, properties, cytopathology, and taxonomy of Potexviruses. Each of the Potexviruses has a fairly narrow host range causing mosaic or ringspot symptoms. Seed transmission is unknown except that both clover yellow mosaic virus and white clover mosaic virus are seed transmitted in Trifolium pretense and possibly in other legumes; foxtail mosaic virus is seedborne in Briza maxima and in oats to a level of 1 to 2%. There are a number of recent reviews of the Potexviruses. Potexvirus particles are flexuous rods with modal lengths ranging from 470 to 580 nm. Potexvirus structure has been studied using electron microscopy of negatively stained particles, either randomly arrayed or oriented in parallel. The virus particles accumulate in the cytoplasm, forming massed aggregates that may exhibit conspicuous banding. Meristematic dome cells may be full of conspicuous aggregates of Potexvirus particles or may be apparently virus-free.