Asthma is one of the commonest respiratory diseases in the United States, affecting approximately 8% of adults. This article reviews the epidemiology, diagnosis, and treatment of asthma, with integration of recommendations from professional societies, with special attention to differential diagnosis. A framework for outpatient management of patients with asthma is presented, including indications for subspecialist referral. With integration of objective diagnostic information, systematic approach through modification of disease triggers and adjustment of controller medications, and patient empowerment to respond to varying symptoms using an asthma action plan, most individuals with asthma are successfully managed in the primary care setting.