The role of infection in asthma is varied in that it may exacerbate established asthma or contribute to the initial development of the clinical onset of asthma. Mounting evidence implicates both roles with particular viral pathogens, namely human rhinovirus and respiratory syncytial virus, among the most likely culprits in asthma inception. Once asthma is present, infection, particularly viral infection, is a common precipitant of asthma exacerbations. Bacterial infections and colonization also have been associated with exacerbation and recurrent wheeze, an effect that may be independent or a cofactor with viruses. Atypical bacterial infections such as Mycoplasma pneumoniae and Chlamydia pneumoniae and fungi in the case of allergic bronchopulmonary aspergillosis, also play a potential role in inducing and exacerbating this disease. In addition, certain individuals may have a genetic predisposition toward viral-induced wheezing and the development of asthma. This article will discuss host and environmental factors, common pathogens, clinical characteristic, and genetic influences associated with infection-related asthma.