Grand Paris Express

The Grand Paris Express (French:; GPE) is a megaproject under construction that comprises new rapid transit lines and extensions of existing lines in the Île-de-France region of France. The project consists of four new lines for the Paris Metro, plus extensions of the existing lines 11 and 14. A total of 200 kilometres (120 mi) of new track and 68 new stations are to be added, serving a projected 2 million passengers a day. It is Europe's largest public transport project. The lines are being built by the (SGP, known until 2023 as the Société du Grand Paris) and will be run by operators chosen by Île-de-France Mobilités, the region's transport authority.

The new lines were originally designated by colour (Red Line, Pink Line, Green Line, Blue Line), but this was changed in 2013 to continue the numbering convention of the Paris Metro. They are therefore now known as lines 15, 16, 17 and 18. The lines are opening in stages between June 2024, when the Line 14 extensions were completed, and 2031.