Boulogne-Billancourt; often colloquially called simply Boulogne is a commune in the western suburbs of Paris, France. It is located 8.2 km (5.1 mi) from the centre of Paris. Boulogne-Billancourt is a subprefecture of the Hauts-de-Seine department and the seat of the Arrondissement of Boulogne-Billancourt. Boulogne-Billancourt is the most populous suburb of Paris and one of the most densely populated municipalities in Europe. Formerly an important industrial site, it has successfully reconverted into business services and is now home to major communication companies headquartered in the Val de Seine business district.