Paris Métro Line 18 in the context of Aéroport d'Orly station

The Grand Paris Express (French: [ɡʁɑ̃ paʁi ɛkspʁɛs]; GPE) is a project consisting of new rapid transit lines and the extension of existing lines being built in the Île-de-France region of France. The project comprises four new lines for the Paris Métro, plus extensions of the existing Lines 11 and 14. A total of 200 kilometres (120 mi) of new tracks and 68 new stations are to be added, serving a projected 2 million passengers a day.

The new lines were originally indexed by colour (Red Line, Pink Line, Green Line, Blue Line), but this was changed in 2013 to continue the numbering convention that the RATP uses. They are therefore now known as Line 15, Line 16, Line 17 and Line 18. The constructed lines are planned to open in stages, starting with the Line 14 extension in June 2024, until 2031.

Paris Métro Line 8 (French: Ligne 8 du métro de Paris) is one of the sixteen lines of the Paris Métro currently opened. It connects Balard (Porte de Sèvres) in the southwestern part of Paris to Pointe du Lac station in the southeastern suburban city of Créteil, prefecture of the Val-de-Marne department, following a parabolic route across Paris. Last line proposed by Fulgence Bienvenüe's original 1898 Paris Métro project, line 8 opened in July 1913 and was initially intended to link Porte d'Auteuil and Opéra. With 105.5 million passengers in 2017, it is the network's eighth busiest line, as well as the current third longest (after Lines 13 and 14, even though Line 13 has a fork, and Line 15 is set to become the longest once fully opened), at 23.4 km (14.5 mi) in length. Alongside Line 7, it serves 38 distinct stations, the most of any line on the network, Grand Paris Express (lines 15 to 18) included. Line 8 interchanges with all other Métro lines but three : Lines 2, 3bis and 7bis.

The line was substantially modified during the 1930s as Line 10 took over the western section from La Motte - Picquet to Porte d'Auteuil. The current route serves the southwestern part of the French Capital, including the Champ de Mars, the Invalides, the Concorde Place, the Opéra Garnier, the Grands Boulevards, The places of République and Bastille as well as the Bois de Vincennes, before ending in the southeastern inner suburbs through the communes of Charenton-le-Pont, Maisons-Alfort and Créteil, which the line reached in 1974 at Créteil–Préfecture station, after several extensions. Line 8 was the first to connect the prefecture of one of the new departments of Île-de-France, more than a decade before Line 5 to Bobigny, and Line 15 to Nanterre in the near-future. Line 8 is also the only Paris underground line to cross the Seine and its principal tributary, the Marne river, above ground via a bridge between Charenton – Écoles and École Vétérinaire de Maisons-Alfort, it also crosses the Seine underground between Concorde and Invalides.