Boulogne-Billancourt is a commune in the western suburbs of Paris, France. It is located 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. With an average household income in 2013 of €47,592, nearly twice the French average of €25,548, Boulogne-Billancourt is one of the wealthiest cities in France. 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.