Poliovirus has attracted immense medical interest in the first 70 years of this century as it has caused epidemics of the dreaded paralytic disease, poliomyelitis. During this period poliovirus became a prototype for animal viruses and was subjected to numerous investigations at the molecular level. These studies revealed properties of the viral genome and mechanisms of viral replication that, when compared to other animal viruses, are unique. Two of the special features of poliovirus structure and replication will be dealt with in this paper: the genome-linked protein VPg, and post-translational, proteolytic processing of viral proteins (for recent reviews, see Rueckert 1976; Korant et al. 1980a; Kitamura et al. 1980a).