The prevalence of asthma is rising globally. Despite the attention asthma has received as a public health issue in the recent past, there are many unanswered questions regarding the aetiology and prevention. The work presented in the monograph has identified some factors that may promote the progression of asymptomatic bronchial hyperreactivity to asthma, established evidence that avoidance of some indoor allergens may play an important role in the prevention of asthma and highlighted the scope for control of those allergens. These findings together with future research, will hopefully enable a more rational and scientific approach to allergen avoidance and prevention of asthma attributable to atopy.