Idiopathic pulmonary fibrosis (IPF) is a progressive, and invariably fatal, condition that is believed to arise in genetically susceptible individuals as a consequence of an aberrant wound-healing response following repetitive alveolar injury. The exact triggers, which initiate the fibrotic process, remain unknown. Infectious agents, including both viruses and bacteria, have the capacity to cause alveolar-epithelial cell injury and apoptosis. Relatively few studies have examined the role of infection in IPF. Those that have, point to viruses playing a key role as cofactors in the initiation and progression of IPF. There is also some evidence to suggest that viral infection may be responsible for a proportion of acute exacerbations of IPF. The role played by bacteria in the pathogenesis of IPF is less clear cut. Studies from other respiratory diseases suggest that alterations in the lung microbiome are associated with disease and that these changes influence disease behaviour. Emerging molecular microbiological techniques are making the study of microbial communities in the lung easier. It is hoped that by combining such techniques with the careful longitudinal phenotyping of patients with IPF, it will be possible to elucidate the role played by bacteria and viruses in the pathogenesis of the disease. If infection plays a causal role in IPF then it is possible that therapeutic strategies, utilising currently available antiviral or antibiotic drugs, may be effective in modifying the course of this devastating condition.