Coat protein (CP) forms the shell of the geminate particles that are typical of begomoviruses. It is the basis of serological detection and identification methods; and it shows a geography-related pattern of variation, as revealed by comparing epitope profiles, determined by reactions with monoclonal antibodies, and deduced amino acid sequences. Its properties include binding to and protecting viral ssDNA, self-binding, nuclear targeting, nuclear export and, with monopartite-genome begomoviruses, mediating systemic movement in plants. CP is needed for transmission by the whitefly vector,Bemisia tabaci . It controls virus transport through the whitefly gut wall into the haemocoele, where it binds a GroEL analogue, produced by a bacterial endosymbiont, in a way that may protect virus particles from degradation. Several properties of CP are determined by the N-terminal third of its sequence, which is also the immunodominant region, but almost all the sequence has been linked to some specific function and much of it is strongly conserved among different begomoviruses. Begomovirus CP is an outstanding example of a multifunctional viral protein.