The relentless increase in the prevalence of asthma and allergic diseases highlights the need for devising effective preventive strategies. Although the genetics of these disorders are being investigated, manipulation of known environmental risk factors remains the best available approach to this problem. However, the large number of potential environmental risk factors and our inability to accurately predict the development of asthma and allergy has led to conflicting data from recent prevention studies. Nonetheless, some useful recommendations can be made. Exclusive breast-feeding and avoidance of exposure to environmental tobacco smoke exposure can be safely recommended for the whole population, not only for prevention of allergy but also for other known benefits. Additionally, for children at high risk of allergy, maternal exclusion diet during lactation and protein hydrolysate as a supplement or alternative for children who could not be breast-fed seems to provide further protection. The preventive effect of avoidance of house dust mite allergen alone during pregnancy or after birth is disappointing. However, prospective randomized studies evaluating a combined food and house dust mite allergen avoidance regimen show some protection against atopic dermatitis in infancy and asthma in later childhood. Urgent research is needed to accurately identify children at high risk and to test novel preventative measures with the potential for immunomodulation. Further randomized controlled trials are also needed with long-term follow up to evaluate combined approaches that might provide maximum benefit.