Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Despite its prevalence, relatively little is known regarding the primary mechanisms of AF and, therefore, current treatment practices focus mainly on controlling the disorder and preventing its complications once it is already present. The study of the pathogenesis of AF is complicated by the varied clinical presentation of the arrhythmia and its coexistence with other cardiac pathologies. This article reviews current efforts to delineate the fundamental mechanisms of AF, with a focus on genetic studies. Identification of the underlying etiology may result in the development of more targeted and effective therapies for AF.