Atrial fibrillation (AF) is a prevalent disease which incidence continues to rise, and concomitantly the associated rates of thrombosis, bleeding, and a general increased burden on our healthcare system. Before this thesis, the quality of contemporary anticoagulation management in Dutch patients with AF was a largely unexplored area. With the results of the GARFIELD-AF registry and the first results of the DUTCH-AF registry, this thesis has provided a first, nationwide insight into Dutch anticoagulation management in AF. Key points of this thesis were the assessment of the extent and determinants of off-label NOAC dosing, the extent of anticoagulation guideline non-adherence and contemporary rates of thrombosis, bleeding, and mortality in Dutch AF patients. In addition, with DUTCH-AF, the foundation for a long-term nationwide AF registry has been created, which will continue to provide us with novel insights into risk factors and (anticoagulation) management in AF. Hereby, we continue to elucidate and expand our knowledge on the implementation, safety and effectiveness of real-world AF treatment, with the aim to identify where further potential improvements in AF care can be made.