Recent years have seen an enormous amount of experimental and clinical research into role of the pulmonary veins (PVs) in atrial fibrillation (AF). Advanced imaging techniques have confirmed the findings of earlier postmortem studies and added further dimension to our knowledge of PV anatomy. Such work is vital for an effective approach to successful ablation of AF. Detailed mapping studies suggest that reentry within the PVs is most likely responsible for their arrhythmogenicity, although focal or triggered activity cannot be excluded. Further work also implicates the posterior left atrium in the genesis of AF. Investigation into the interplay between the PVs and left atrium has led to a reevaluation of the mechanisms underlying AF and suggests that the PVs may play a role in both the initiation and maintenance of this arrhythmia. In order for electrophysiologists to further develop the technical approach to ablation of AF and improve the clinical outcomes, these crucial issues must be resolved.