The supraventricular arrhythmias include a wide spectrum of disorders including, in descending order of frequency, atrial fibrillation, atrial flutter, atrioventricular nodal reentry, Wolff-Parkinson-White syndrome, and atrial tachycardia. While not life-threatening in most cases, they may cause important symptoms, such as palpitations, chest discomfort, breathlessness, anxiety, and syncope, which significantly impair quality of life. Medical therapy has variable efficacy, and most patients are not rendered free of symptoms. Research over the past several decades has revealed fundamental mechanisms involved in the initiation and maintenance of all of these arrhythmias. Knowledge of mechanisms has in turn led to highly effective surgical and catheter-based treatments. Atrial fibrillation remains a therapeutic challenge but is also yielding to investigation and therapeutic efforts. The supraventricular arrhythmias and their treatment are described in this report.