Occupational asthma (OA) is an important cause of adult onset asthma and may contribute particularly to severe asthma. There are two major forms of OA: (1) OA with latency that develops after sensitization to workplace antigens and (2) irritant-induced asthma that develops from direct effects of an irritant on the airway. A number of host and environmental factors will determine whether an individual develops OA. Appropriate evaluation requires systematic monitoring in and outside the workplace. Patients with OA should be managed with environmental control, ideally eliminating all exposure to the agent causing the asthma. Asthma may persist even after removal from the agent that caused the disease.