The relationship between asthma and infectious disease has long been studied. The Advisory Committee on Immunization Practices in U.S. has recently recommended a pneumococcal polysaccharide vaccine to adults with asthma ages 19-64 years. This recommendation is based on 2 large epidemiologic studies which reported that individuals with asthma carry an increased risk of invasive pneumococcal diseases. There have been some reports which stated that asthma is the most common chronic disease in individuals who have been infected with novel H1N1 influenza virus, suggesting the potential role of asthma in infections. However, it is unclear how asthma increases the susceptibility of infections. Several mechanisms have been proposed, including disruption of the airway epithelium, increased and aberrant mucus production, and alterations in innate or adaptive immunity. This paper was conducted to examine the epidemiological relationship between asthma and infectious disease and to investigate the possible mechanisms and their implications in clinical practice, public health and research.