RNA silencing is a conserved eukaryotic process mediated by small RNA molecules that inhibit gene expression at the transcriptional, mRNA-stability or translational level through sequence-specific interactions. Diverse roles have been identified for RNA silencing such as genome defense against mobile DNA elements or down-regulation of specific factors during plant and animal development. In plants, RNA silencing plays a crucial role in antiviral defense by inhibiting viral accumulation and sometimes preventing systemic infection. As a counter-defense mechanism, viruses have evolved anti-silencing strategies through the production of viral suppressors of RNA silencing. Here we review the mechanism of RNA silencing and its inhibition during plant/virus interactions and suggest the possible consequences of this molecular arms race on the evolution of both viral and host genomes.