The order Reovirales previously known as the family Reoviridae contains double-strand RNA viruses, which infect wide range of organisms including arthropods, primates, fish, birds, reptiles, algae, fungi, insects, and plants. The Reoviridae is recently split into two families by the ICTV as Spinareoviridae and Sedoreoviridae, containing a total of 15 genera and 97 species. Of these, three genera Fijivirus, Oryzavirus, and Phytoreovirus are plant infecting arboviruses and the remaining infect other hosts. Only plant-infecting reoviruses are described in this chapter. The name Reovirales is derived from the word respiratory enteric orphan disease, as the viruses caused respiratory and enteric infections but believed not associated with the disease, hence they were considered “orphan” viruses. The family Sedoreoviridae (Matthijnssens et al. 2022a) got its name from sedo, Latin for “smooth”, indicating the absence of spikes or turrets on the surface of the core particles and a smooth appearance. In contrast, the family Spinareoviridae (Matthijnssens et al. 2022b) gets its name from spina that is Latin for “spike” and refers to the presence of spikes or turrets on the surface of the core particles. Members of both families of the Reovirales have particles with icosahedral symmetry but can also be spherical. The protein capsid is organized as one, two, or three concentric layers of capsid proteins surrounding the linear dsRNA genome with 9–12 segments and a total diameter of 60–95 nm. The main differences between the families are: (i) members of Sedoreoviridae do not have large surface protrusions on their virions or core particles, giving them an almost spherical or “smooth” appearance. Members of Spinareoviridae, on the other hand, contain relatively large spikes or turrets on the 12 icosahedral vertices of the virion or core particle. (ii) The Sedoreoviridae have a double-layered core without surface spikes and are surrounded (when the virions are intact) by an outer capsid shell, giving rise to triple-layered virions, whereas the Spinareoviridae have double-layered particles. These two families are described together in this single chapter here because of few phytoreoviruses (only 3 genera), their high similarities, and historical description as a single family.