There is abundant evidence that asthma is frequently exacerbated by infectious agents. Several viruses have been implicated in the inception and exacerbation of asthma. Recent attention has been directed at the role of infections with the atypical bacteria Mycoplasma pneumoniae and Chlamydia pneumoniae as agents capable of triggering asthma exacerbations and potentially as inciting agents for asthma. This article examines the evidence for interaction between specific infectious agents and exacerbations of asthma, including the immunopathology of infection-triggered asthma, and the current therapeutic options for management.