The SNCF Class Z 20500 is a double-deck, dual-voltage electric multiple unit trainset that are operated by SNCF on the Réseau Express Régional (RER), a hybrid suburban commuter and rapid transit system and the Transilien, a suburban commuter rail system, both serving Paris and its Île-de-France suburbs.

[4] The equipment received some modifications to make them suitable for one operator and then deployed on Transilien Line P. this link leads to the Z20500 fleet page (in french) Z20500 fleet The Z20500 resumes the general architecture of Z5600 / Z8800, drawn by MBD design, having more angular shapes.

Many liveries have existed according to the renovations and wishes of the organizing authority : The interior is composed of two intermediate platforms at the ends and a two-level section in the center.

The SIVE, "Système d'information voyageurs embarqué" (On-board passenger Information System) is also installed, made up at first of audio announcements (only for the trains running on the RER D), then since 2011, visual devices and Closed-circuit television.

In 2018 begins the renovation 2 (2018 -), The purpose of this work is to improve thermal comfort by affixing athermic films on the windows and by increasing the number of opening windows, to make improvements to the interior fittings (resumption of degraded upholstery, new lamination of the ceilings, replacement of all the seat fabrics, equipment of the platforms with USB sockets, etc.)