The German Competence Network on Atrial Fibrillation (AFNET) is an interdisciplinary national research network funded by the Federal Ministry of Education and Research (BMBF) since 2003. The AFNET aims at improving treatment of atrial fibrillation (AF), the most frequent sustained arrhythmia of the heart. The AFNET has established a nationwide patient registry on manifestation, diagnostics, and therapy of AF in Germany. The data analyzed to date demonstrate that patients with AF are likely to have multiple comorbidities (hypertension, valvular heart disease, coronary artery disease, diabetes mellitus) and an advanced age. Regarding oral anticoagulation, guideline adherence is very high. Basic research has identified specific changes in atrial tissue during AF-induced remodeling providing the rationale for novel therapeutic interventions. Clinical trials are being carried out to optimize pharmacological and nonpharmacological treatments. The ANTIPAF trial is designed to prove that angiotensin II receptor blockers reduce the incidence of paroxysmal AF. The Flec-SL trial tests the efficacy of a short-term treatment with antiarrhythmic drugs after cardioversion. The Gap-AF trial investigates the impact of complete pulmonary vein (PV) isolation versus incomplete circumferential PV ablation on AF recurrences. The effect of preventive pacing on the recurrence of paroxysmal AF is studied in the BACE-PACE trial.