RecruitingNHALES (Natural History of Asthma With Longitudinal Environmental Sampling)Background: \- Asthma is a serious clinical and public health problem. Researchers want to collect data to better understand how bacteria and other things in the environment can affect people's asthma. Eligibility: \- Nonsmoking adults age 18 - 60 who have moderate to severe asthma. Design: * Participants will complete a medical history form before the first visit. * Study visits will include collecting medical history, and conducting physical exam, lung and smoking tests. Participants will give blood, urine, stool, dust, saliva, and sputum samples. * Participants will take tests that measure their breathing abilities. They will give saliva samples for DNA study. They will get kits to collect stool and dust samples at home. They will fill out surveys. * Participants will have visits every 6 months for 5 years. They can schedule sick visits, if needed, at no cost to the participant. For all visits, they will have asthma check-ups and get treatment, at no cost to the participant. * Some participants may take part in a sub-study that includes one 4-hour visit. They will have medical history, physical exam, and lung tests. They will have urine tests to check for pregnancy and tobacco exposure. Then they will have bronchoscopy. For this, an intravenous line will be placed in an arm vein. The nose and throat will be numbed. A flexible fiber-optic tube will be inserted into their airways through the nose. Their airways will be examined and areas of their lung will be washed. A small sample of cells will be taken.