Several key conditions that are necessary to identify disease susceptibility genes in common diseases such as asthma are now available. Collectively, these conditions will allow the prioritization of candidate genes based on available knowledge of map position and biologic relevance; obtain genomic structure of these genes; and study sequence variants in these genes in populations to facilitate the identification of genes that are important in the development and expression (severity) of asthma and associated phenotypes. Although, it is still a labor-intensive and expensive project to identify susceptibility genes in common diseases such as asthma, the new techniques that are now being used will greatly facilitate gene mapping.