The 100 Series are a series of underground railway cars manufactured by Alstom in Brazil and Argentina for use on the Buenos Aires Underground. They are used on Line D of the network, where they make up the vast majority of the fleet, serving alongside some 300 Series and Fiat-Materfer cars. Since 2019, some units have also been used on the Line E.

The Buenos Aires Underground, locally known as Subte, is a rapid transit system that serves the area of the city of Buenos Aires, Argentina. The first section of this network opened in 1913, making it the 13th earliest subway network in the world and the first underground railway in Latin America, the Southern Hemisphere, and the Spanish-speaking world, with the Madrid Metro opening five years later, in 1919. As of 2023, Buenos Aires is the only Argentine city with a metro system.