Boulogne-Billancourt is a commune in the western suburbs of Paris, France. It is located 8.2km 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.NameThe original name of the commune was Boulogne-sur-Seine .Before the 14th century, Boulogne was a small village called Menuls-lès-Saint-Cloud . In the beginning of the 14th century, King Philip IV of France ordered the building in Menuls-lès-Saint-Cloud of a church dedicated to the virgin of the sanctuary of Boulogne-sur-Mer, then a famous pilgrimage center in northern France. The church, meant to become a pilgrimage centre closer to Paris than the distant city of Boulogne-sur-Mer, was named Notre-Dame de Boulogne la Petite . Gradually, the village of Menuls-lès-Saint-Cloud became known as Boulogne-la-Petite, and later as Boulogne-sur-Seine.