12 rue de Prony was built in 1879, in the Neo-Renaissance style, by the celebrated architect Jean-Louis Pascal for the Austrian Baron, Jonas Königswater, a former banker and railway owner. A succession of major works to renovate and modernise the headquarters were undertaken by the Directors General elected after E.Leclainche: Gaston Ramon, René Vittoz, Louis Blajan, Jean Blancou and Bernard Vallat. Due to the headlong development of the organisation (tripling of the staff and the budget since 2001), additional premises have been rented at 14 rue de Prony since 2004. On 16 March 2009, the OIE purchased a large part of the building at 14 rue de Prony, adjoining its headquarters.