This chapter provides a brief account of the development of studies on structure, composition, properties, cytopathology, and taxonomy of Tobraviruses. The Tobravirus group is named after the type member, tobacco rattle virus (TRV). The viruses are soil-borne and may sometimes invade only the roots of plants. Viruses in the group have divided genomes consisting of two positive-sense, single-stranded RNA segments. The group consists only of TRV and pea early browning virus and their strains. Tobraviruses appear to multiply in the cytoplasm of infected plants and of protoplasts. The characteristic particles of Tobraviruses are very evident in thin sections of infected tissues, and their structure resembles that of embedded and sectioned purified virus. The ability of the different genome segments of a virus to complement one another in artificial mixtures (pseudorecombination) is an indicator of whether or not the components come from closely related virus strains.