Double-stranded RNA (dsRNA) viruses are a diverse group of viruses infecting hosts from bacteria to higher eukaryotes. Among the hosts are humans, domestic animals, and economically important plant species. Fine details of high-resolution virion structures have revealed common structural characteristics unique to these viruses including an internal icosahedral capsid built from 60 asymmetric dimers (120 monomers!) of the major coat protein. Here we focus mainly on the structures and assembly principles of large icosahedral dsRNA viruses belonging to the families of Cystoviridae and Reoviridae. It is obvious that there are a variety of assembly pathways utilized by different viruses starting from similar building blocks and reaching in all cases a similar capsid architecture. This is true even with closely related viruses indicating that the assembly pathway per se is not an indicator of relatedness and is achieved with minor changes in the interacting components.