The versatility of ubiquitin in regulating protein function and cell behaviour through post-
translational protein modification makes it a particularly attractive target for viruses. Here we
review how viruses manipulate the ubiquitin system to favour their propagation by
redirecting cellular ubiquitin enzymes or encoding their own ubiquitin components to enable
replication, egress and immune evasion. These studies not only reveal the many cellular
processes requiring ubiquitin but also illustrate how viruses usurp their host cells.