Asthma is a complex and heterogeneous disease involving many genes and environmental factors. Numerous genetic association studies of asthma, atopy and bronchial hyper-responsiveness have consistently implicated a small number of genes, most of which are involved in immune responses. Genome-wide screens of various populations in the past three years have identified six asthma and/or atopy susceptibility genes by means of positional cloning. However, the precise functions of these genes are unclear. Recent advances in molecular methods for genotyping thousands of polymorphisms in candidate regions (and, very soon, across the entire genome), together with new statistical methods applicable to complex biological systems, will rapidly identify new culprit genes as well as gene-gene and gene-environment interactions. A better knowledge of asthma susceptibility will lead to better diagnosis, prevention and treatment of this increasingly frequent disease.