Boulogne-Billancourt is a commune in the western suburbs of Paris, located 8 km from its centre. It is a subprefecture of the Hauts-de-Seine department and thus the seat of the larger arrondissement of Boulogne-Billancourt. It includes two large islands in the Seine: Île Saint-Germain and Île Seguin. With a population of 121,334 as of 2018, it is the department's most populous commune. Boulogne-Billancourt is the most populous suburb of Paris, as well as one of the most densely populated municipalities in Europe.
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 communes in France. 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.
