Each and every virus is a unique and highly complex system. The complexity is hugely increased when one considers also interactions of viruses with its host and, for vector transmitted viruses, with the arthropod vector. Our research focus has been RNA replication process/enzymes/complexes of positive-strand RNA viruses. As genome replication and gene expression represent the central event for infection cycle of a virus it effects directly or indirectly all other aspects of biology of viruses.