Every day in the United States, 40,000 people miss school or work due to asthma. Since the 1980s, the number of asthma cases has been increasing worldwide. Though there is no cure for asthma, treatment and avoidance of asthma triggers can keep the disease under control for most people. If a parent has asthma, there is a one-in-three chance his or her child will develop asthma. But inheriting asthma is not as simple as a single 'asthma gene'. An entire set of genes is involved, combined with the exposure to certain substances in the environment. Asthma researchers are making exciting and complex discoveries about the genetic and environmental causes of asthma, which may eventually lead to asthma prevention. Advances in genetic engineering techniques provide new tools for developing treatments that can be customized for a variety of forms of asthma. ""Asthma"" describes the complex relationships among genes, the environment, and asthma, and how scientists are using this information to improve the lives of people dealing with asthma.