[10] Since November 2024 it has also been leading (51%) the operation of the Thessaloniki Metro in partnership with Egis Group (49%).
[11] Public transport in Milan started on August 17, 1840, with the opening of the Milan-Monza railway.
Few years later the first horse-drawn trams were introduced: 3 lines were opened in 1881 followed in 1893 by the first electric tramway, built by Edison company.
In the meantime, the first petrol powered bus lines were introduced in 1905, operated by SITA (Società Italiana Trasporto con Automobili) and then moved under control of ATM along with the first trolleybus line (1933).
After World War II resources were focused on bus lines and, since the mid-1950s, on the new metro.
On 1 January 1965, ATM changed its name to "Azienda Trasporti Municipali" (Municipal Transport Company).
ATM changed its name again in 1999 to adopt the current one, "Azienda Trasporti Milanesi", and it became a S.p.a. in 2001.
ATM operates a single people mover line, MeLA, that connects the Milan Metro with San Raffaele Hospital.