Activation of the nuclear factor (NF)-kappaB transcription factor family in response to different stimuli, such as inflammatory cytokines, stress inducers or pathogen products, results in host innate and adaptive immunity. NF-kappaB plays a central role in promoting the expression of genes involved in inflammatory, immune and apoptotic processes, including those encoding cytokines, chemokines, cytokine receptors and proteins involved in antigen presentation. Although the main function of NF-kappaB is to activate specific genes in the cells of the immune system, its role in controlling the host cell cycle makes NF-kappaB an interesting target for pathogenic viruses. Some viruses take advantage of the anti-apoptotic properties of NF-kappaB to escape host defence mechanisms, others use apoptosis to spread. This review describes the role of the NF-kappaB family in immune responses, the mechanism of NF-kappaB activation, and different strategies that viruses have developed to modulate the NF-kappaB pathway in order to facilitate and enhance viral replication and avoid host immune responses.