Acute atrial fibrillation (AF) is the most common cardiac rhythm encountered in clinical practice and is commonly seen in acutely ill patients in critical care. In the latter setting, AF may have two main clinical sequelae: (1) haemodynamic instability and (2) thromboembolism. The approach to the management of AF can broadly be divided into a rate control strategy or a rhythm control strategy, and is largely driven by symptom assessment and functional status. A crucial part of AF management requires the appropriate use of thromboprophylaxis. In patients who are haemodynamically unstable with AF, urgent direct current cardioversion should be considered. Apart from electrical cardioversion, drugs are commonly used, and Class I (flecainide, propafenone) and Class III (amiodarone) antiarrhythmic drugs are more likely to revert AF to sinus rhythm. Beta blockers and rate limiting calcium blockers, as well as digoxin, are often used in controlling heart rate in patients with acute onset AF. The aim of this review article is to provide an overview of the management of AF in the critical care setting.