Viruses are obligate parasites which can infect cells of all living organisms. Multiple antiviral defense mechanisms appeared early in the evolution of the immune system. Higher vertebrates possess the most complex antiviral immunity based on both innate and adoptive immune responses. However, a majority of living organisms, including plants and invertebrates, rely exclusively on innate immune mechanisms for protection against viral infections. There are some striking similarities in several components of innate immune recognition in mammals, plants, and insects suggesting that these signaling cascades are highly conserved in the evolution of the immune system. This review summarizes recent advances in the field of innate immune recognition of viruses, with a focus on pattern-recognition receptors.