Construction of the original sections (as well as the extension towards République) proved to be difficult due to public opposition in the various arrondissements as well as unstable soil above the tunnels.

Public support for the line's construction was greatly difficult due in part to proposed sections that various entities saw as impossible to build and operate under government regulations at the time.

The double-decker tunnel, which is located between stations Richelieu - Drouot and République (and carries Line 9 on the lower level, while Line 8 is situated on the upper level) was especially problematic due to unstable ground at Grand Boulevards.

(from fr:Ligne 9 du métro de Paris) Line 9 is operated with the MF 01 stock in five-car sets.

The €330 million order began deliveries during June 2013 and will continue through 2016 to replace the current stock on line 9.