The Siemens Modular Metro is a family of electric multiple unit trains for rapid transit systems produced by Siemens Mobility and used by rail operators around the world. The vehicle concept was launched in Vienna in 2000 and is a modular concept allowing many variants of metro vehicles. Previously known as Modular Mobility, Siemens, whose rail equipment division had since been renamed Siemens Mobility, still uses the abbreviation Mo.Mo; however, very little more of these trains are being built, since Siemens had moved to their Inspiro metro platform in 2013.

Siemens Mobility is a division of Siemens. With its global headquarters in Munich, Siemens Mobility has four core business units: Mobility Management, dedicated to rail technology and intelligent traffic systems, Railway Electrification, Rolling Stock, and Customer Services.