Atrial fibrillation and atrial flutter are the most common dysrhythmias seen in the emergency department. As the aging population continues to grow, atrial fibrillation and atrial flutter are expected to affect 6 million people by 2050. This will lead to an increase in emergency department visits for symptoms from the disease itself or its complications, such as heart failure or thromboembolic disease. This review examines the recent literature on the diagnosis and management of atrial fibrillation. Evidence-based recommendations are provided, including cost-effective strategies to evaluate new-onset arrhythmias and unstable patients with atrial fibrillation, rate control strategies, the use of medical and direct current cardioversion for new-onset atrial fibrillation/atrial flutter, whom and when to anticoagulate, and the use of the novel anticoagulation agents.