MicroRNAs (miRNAs) are an important class of small, noncoding, regulatory RNAs found to be involved in regulating a wide variety of important cellular processes by the sequence-specific inhibition of gene expression. Viruses have evolved a number of mechanisms to take advantage of the regulatory potential of this highly conserved, ubiquitous pathway known as RNA interference (RNAi). This review will focus on the recent efforts to understand the complex relationship between vertebrate viruses and the RNAi pathway, as well as the role of silencing pathways in the inhibition of pathogenic genetic elements, including transposons and retrotransposons.