Atrial fibrillation (AF) occurs predominantly in the elderly and is commonly associated with underlying cardiac diseases. A significant number of patients, however, have early onset AF that is not associated with any underlying disease. At present, it is unknown how often this form of AF is familial and how frequently familial AF is due to genetic causes. Recent data suggest that familial AF occurs more frequently than previously recognized. Also, in AF in the setting of underlying diseases, it is suggested that some form of genetic control may be present. Understanding the molecular mechanisms underlying AF may provide insight into the pathogenesis of AF and eventually may lead to improved, patient-tailored rhythm control strategies.