Atrial fibrillation is the subject of much clinical interest as it is the arrhythmia responsible for the greatest number of hospital admissions. The arrhythmia working group of the French Society of Cardiology held a symposium on atrial fibrillation in order to establish certain definitions and to assess the value of a classification of atrial fibrillation. This was also the occasion to review a number of known facts and points which remain obscure, concerning this common arrhythmia. A therapeutic strategy is proposed.