Asthma and allergic diseases are complex conditions caused by a combination of genetic and environmental factors. More than 100 genes have been associated with asthma and related conditions through candidate gene approaches, but issues of insufficient replication have made conclusions difficult to draw. Despite this, several overarching themes in the biology and pathogenesis of asthma have been revealed as a result of this work. In mid-2007, the first genome wide association study (GWAS) targeting asthma was published, and in the intervening years more than a dozen such studies have been reported examining asthma, allergic diseases, and related intermediate phenotypes and quantitative traits. A few previously suspected genetic variants have been confirmed in these studies as asthma susceptibility loci, or as loci contributing to disease severity or response to treatment. Additionally, unexpected and largely uncharacterized genes have been identified as new susceptibility loci for asthma, altering lung function or perturbing immune function. In this review, we summarize these GWAS, as well as the functional themes and characteristics underlying asthma that have been revealed through decades of genetic and genomic research.