The term “X'Trapolis” designates a series of mainly electric multiple units built by Alstom for Metro and commuter services. The X'Trapolis 100 is a single-deck variant with two or three cars for use under 1,500 Volts DC. While two-car sets have one car with four 180 kW traction motors, three-car sets have two powered cars. They are designed to operate in multiple of two units as standard, i.e. with four or six cars.

In 2002, the first three-car trains were delivered to Melbourne for the Hillside Trains network. After the first batch, a second batch was built between 2009 to 2020. This made a total of 212 sets which are also being used on other lines. Valparaíso in Chile started to build a completely new Metro system in 1999 and also ordered the X'Trapolis. The first of a total of 27 two-car sets were delivered in 2005.