The prevalence of atrial fibrillation (AF) increases with age. Recent population-based data indicate a trend of increasing incidence and prevalence of AF that is incompletely explained by an aging population. A recent population study estimated that the number of Americans afflicted by AF will increase from the current 2.3 million to more than 10 million by 2050. Novel risk factors—obesity and sleep apnea—may partially account for the current AF epidemic. Ethnic differences in the epidemiology of AF have been suggested but not clearly elucidated by population-based studies. The heritability of AF in the general population is strongly supported by population-based data. Genetic epidemiological studies on AF can potentially yield important mechanistic insights that may ultimately lead to novel preventative and therapeutic strategies.