Responses to the three major classes of asthma therapy, beta-agonists, leukotriene antagonists and inhaled corticosteroids, demonstrate wide inter-individual variability. Moreover, both asthma and the traits measured in response to asthma therapy, including forced expiratory volume at 1 s, are highly heritable. This indicates that genetics may play a prominent role in the determination of the therapeutic response to asthma. The human genetic association trials that investigate responses to each of the three major classes of asthma therapy will be summarized, and recent findings in the literature highlighted. Altogether, the available data indicate that genetics influences the likelihood of an individual responding to a given therapy, indicating that, in the future, optimal care for individuals with asthma may include genetic testing.