Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. It is common in the elderly and those with structural heart disease. Clinical classification can be helpful in treatment decisions and the most widely accepted classification scheme (first episode, recurrent paroxysmal, recurrent persistent, permanent) is found in the ACC/AHA/ESC guidelines. The pathophysiology of AF remains unclear at this time. It is unlikely that a single pathophysiology is operative in all or even a majority of cases. Therapies to be considered for AF include prevention of thromboembolism, rate control, and restoration and maintenance of sinus rhythm. These therapies and specific treatments for these purposes are discussed under these headings, including a section on the relative merits of the rate control and rhythm control strategies. Risk stratification is a fundamental part of the treatment for thromboembolism. When risk warrants treatment, prevention of thromboembolism is achieved either pharmacologically with aspirin, or with warfarin or new agents like ximelagatran, or by nonpharmacological approaches. Schema to assist in risk stratification and selection of appropriate antithrombotic therapy are provided. Recent trials comparing the strategy of rate control to the strategy of rhythm control failed to demonstrate that the rhythm control approach is superior to the rate control approach in patients and therapies studied so far. Rate control is an acceptable primary line of therapy in many patients, particularly the elderly with persistent AF who are not highly symptomatic. However, the risk and benefit of each treatment modality should be individualized according to the patient circumstances and comorbidity. Algorithms to help individualize which of the two strategies to use are provided. There are a number of pharmacologic and nonpharmacologic therapies available for rhythm management of AF. Pharmacologic cardioversion is an alternative to electrical cardioversion for recent onset AF but the latter is preferred for persistent AF. Current drug therapy to maintain sinus rhythm is neither highly effective nor completely safe. An algorithm to guide selection of the most appropriate antiarrhythmic drug for an individual patient is provided. Nonpharmacologic therapies for maintenance of sinus rhythm include surgery, radiofrequency ablation, devices, and hybrid (combination) therapies. Much remains to be learned about the role and application of such therapies. Pharmacologic heart rate control can be achieved for most patients with available agents and, when it cannot, there are effective nonpharmacologic therapies. A few specific situations in which AF occurs and for which there are some special considerations are described.