Virtually all studies of structure and assembly of viral filaments have been made on plant and bacterial viruses. Structures have been determined using fiber diffraction methods at high enough resolution to construct reliable molecular models or several of the rigid plant tobamoviruses (related to tobacco mosaic virus, TMV) and the filamentous bacteriophages including Pf1 and fd. Lower-resolution structures have been determined for a number of flexible filamentous plant viruses using fiber diffraction and cryo-electron microscopy. Virions of filamentous viruses have numerous mechanical functions, including cell entry, viral disassembly, viral assembly, and cell exit. The plant viruses, which infect multicellular organisms, also use virions or virion-like assemblies for transport within the host. Plant viruses are generally self-assembling; filamentous bacteriophage assembly is combined with secretion from the host cell, using a complex molecular machine. Tobamoviruses and other plant viruses disassemble concomitantly with translation, by various mechanisms and involving various viral and host assemblies. Plant virus movement within the host also makes use of a variety of viral proteins and modified host assemblies.