In Western countries, the prevalence of asthma has increased during the last decades. Although asthma is often non-lethal, the quality of life of patients is seriously affected and there is still no definitive cure available. It is clear that the environment has a dramatic impact on the incidence and the severity of allergy and asthma, and a strong link between respiratory tract infections and asthma has been demonstrated, with some viruses being able to induce an exacerbation of symptoms in asthmatic patients. Moreover, a number of epidemiological studies have shown that severe respiratory syncytial virus (RSV) infections in infants can provide the foundations for the development of chronic asthma later in life. Although these associations are clearly established, the underlying mechanisms are currently largely unknown, mostly due to the lack of relevant animal models. Recently, novel models have been developed that clinically better mimic respiratory virus infections and asthma, and we therefore believe that it is now time to study the link between these diseases in a thorough way. By gaining more insights in the foundations of asthma, we aim to find novel and better targets for treating and/or preventing allergic asthma.