The SNCF Class Z 20900 is a double-deck, dual-voltage electric multiple unit trainset that is operated on line C of the Réseau Express Régional (RER), a hybrid suburban commuter and rapid transit system serving Paris and its Île-de-France suburbs.

The 54 four-car trains were built by a consortium of French manufacturer Alstom and Canadian conglomerate Bombardier between 2001 and 2004.

They are the final equipment produced as part of the Z 2N series of trainsets, which were continuously improved over several generations.

SNCF ordered the Class Z 20900 at the end of 1998 to complete the rolling stock fleet of line C and to replace the last 42 Z 5300 units still in service.

The design of 54 four-car trainsets would be based on the earlier Z 20500.They are distinguished in particular by : The two power cars (ZB) have 82 seats while the two trailers (ZRB) each have 96, as well as a toilet.