Asthma in the US is widespread, with incidence rates and morbidity increasing dramatically over the last 2 decades. The cost of asthma-related morbidity and mortality is large. There is substantial and convincing evidence that environmental factors are associated with asthma exacerbation, and more limited evidence that environmental factors play a role in the development of asthma. Educational interventions, which include an avoidance of ‘triggers’ or focus on reducing exposure to cigarette smoke, have been shown to be moderately effective. While various interventions have been shown to reduce environmental exposures, fewer studies have collected sufficient information on their effectiveness in reducing morbidity.Cost-effectiveness analyses on educational interventions suggest that reductions in direct costs are most prominently seen for severe asthma, with the interpretation of study findings impaired by a lack of methodological consistency. One analysis from a study that included physical interventions found that the incremental cost-effectiveness ratio was $US9.20 per symptom-free day (95% CI −$US12.56, $US55.29), with potential cost savings for more severe asthma.We point out that current practice in managed care organizations (MCOs), as well as in other settings, rarely conforms to the current clinical practice guidelines for asthma. Two reviews of the policies and actions of MCOs found that while some were integrating environmental controls into their asthma disease management plans, their commitment to these strategies was limited by lack of a strong evidence base.We recommend the following:continuation of educational programs;continuation and expansion of case management, including home visits;full integration of smoking cessation programs into asthma disease management;development of policies around reimbursement for durable goods;participation in the setting of a policy agenda for population-based approaches to controlling key environmental factors;development of exploratory programs to address occupational asthma;integration, analysis and dissemination of environmental data collected by MCOs; andwidespread MCO participation in research on environmental prevention of asthma.