Atrial fibrillation is the most common cardiac arrhythmia. This issue of Cardiology Clinics examines following facets of atrial fibrillation: epidemiology and societal impact, risk factors and genetics, mechanisms, diagnosis and follow-up, rate versus rhythm control, antiarrhythmic drug therapy, catheter ablation, surgery, antithrombotic and anticoagulant therapy, left atrial appendage exclusion, management of patients with heart failure and structural heart disease, and novel treatment paradigms.