Toll-like receptors (TLRs) have evolved to recognize conserved features of microbial pathogens, including bacteria, viruses, fungi, and protozoa. Among these pathogen classes, viruses are particularly vexing, as they generally lack any uniquely foreign features that easily distinguish them from the host. Consequently, a number of TLR family members have evolved to recognize various forms of viral nucleic acid. The emergence of this specificity has interesting implications for how we view the evolution of viral genomes. In this review, I discuss the various strategies used by TLRs to recognize viruses as well as the experimental evidence implicating TLRs in viral immunity.