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.