The MP 89 is a rubber tired variant of electric multiple units used on the Paris Métro. Designed by Roger Tallon, two types are built by GEC-Alstom for service on Lines 4 and 14, and has begun service on Line 6. The trains on Line 1 were moved to Line 4 between 2011 and 2013 to replace the older MP 59s, though only 48 trains are used for revenue service. The remaining four trains are stored either at Montrouge or Saint Ouen as operational spares.

Line 4 is one of the sixteen lines of the Paris Métro rapid transit system and one of its three fully automated lines. Situated mostly within the boundaries of the City of Paris, it connects Porte de Clignancourt in the north and Bagneux-Lucie Aubrac in the south, travelling across the heart of the city. Until its southern terminus was changed from Porte d'Orléans to Mairie de Montrouge in 2013, the line was sometimes referred to as the Clignancourt – Orléans Line. At 13.9 km (8.6 mi) in length, it connects with all Paris Métro lines apart from the very short 3bis and 7bis branch lines, as well as with all 5 RER express lines. It also serves three of the Paris Railway stations, Gare du Nord, Gare de l'Est, and Gare Montparnasse. It is the second-busiest Métro line after Line 1, carrying over 154 million passengers in 2004.