The prevalence of asthma continues to increase throughout Western societies and now is estimated to affect nearly 10% of Americans. Asthma is a syndrome that results when a genetically susceptible individual is exposed to specific allergens, which triggers airway inflammation, bronchial hyperresponsiveness, and airway remodeling. Family and twin studies have shown that there is a major genetic component to the development of asthma and have attempted to determine the heritable risk. Linkage analysis has identified several areas of interest on multiple different chromosomes that have been associated with different asthma phenotypes. Candidate gene studies have looked at specific gene polymorphisms that are associated with the development of asthma. Finally, several genes are associated with the development of asthma in response to specific environmental allergen exposures. Asthma is a heterogeneous collection of diseases that can result from multiple different pathological processes. The inheritance of asthma is complex and not due to a single gene mutation. Rather, asthma appears to be the result of multiple genetic mutations that influence an individual's susceptibility to develop asthma in response to specific allergens.