In plants the mechanism of RNA silencing evolved to defend plants against viral infection as well as to regulate gene expression for growth and development. However, viruses counteract this antiviral defence expressing silencing suppressor proteins, which are potent arms in the arms race between plants and invading viruses. Our better understanding of the molecular bases of the induction and the suppression of RNA silencing dramatically improved our basic knowledge about intimate plant-virus interactions and also provide valuable tools to unravel the diversity, regulation and evolution of RNA-silencing pathways.