The Milan Metro (Italian: Metropolitana di Milano) is the rapid transit system serving Milan, Italy, operated by Azienda Trasporti Milanesi. The network consists of five lines with a total network length of 111.8 kilometres (69.5 mi), and a total of 125 stations (+2 in construction), mostly underground. It has a daily ridership of about 1.4 million on weekdays. The Milan Metro is the largest rapid transit system in Italy in terms of length, number of stations and ridership; and the fifth longest in the European Union and the eighth in Europe.

The first line, Line 1, opened in 1964; Line 2 opened 5 years later in 1969, Line 3 in 1990, Line 5 (driverless) in 2013, and Line 4 (driverless) in 2022. There are also several extensions planned and under construction. The architectural project of the Milan Metro, created by Franco Albini and Franca Helg, and the signs, designed by Bob Noorda, received the Compasso d'Oro award in 1964.

The first projects for a subway line in Milan were drawn up in 1914 and 1925, following the examples of underground transport networks in other European cities such as London and Paris. Planning proceeded in 1938 for the construction of a system of 7 lines, but this too halted after the start of World War II and due to a lack of funds.

On 3 July 1952, the city administration voted for a project of a metro system and on 6 October 1955, a new company, Metropolitana Milanese, was created to manage the construction of the new infrastructure. The project was funded with ₤ 500 million from the municipality and the rest from a loan. The construction site of the first line was opened in viale Monte Rosa on 4 May 1957. Stations on the new line were designed by Franco Albini and Franca Helg architecture studio, while Bob Noorda designed the signage. For this project both Albini-Helg and Noorda won the Compasso d'Oro prize.

The first section from Lotto to Sesto Marelli (21 stations) was opened on 1 November 1964 after 7 years of construction works. Two trains adorned with Italian flags left at 10.41 a.m. and arrived at the Sesto Marelli terminus at 11.15 a.m., greeted by the notes of the national anthem and the triumphal march of Giuseppe Verdi's opera "Aida". The track was 12.5 km (7.8 mi) long, and the mean distance between the stations was 590 m (1,940 ft). In the same year, in April, works on the second line started. Passengers on the network grew constantly through the first years of service, passing from 37,092,315 in 1965 to 61,937,192 in 1969.

The green line from Caiazzo to Cascina Gobba (7 stations) opened five years later. During the 1960s and 1970s, the network of 2 lines was completed, and both lines had 2 different spurs. In 1978, the lines were already 17.6 km (10.9 mi) and 23 km (14 mi) long respectively, with 28 and 22 stations.

The first section of the third line (yellow), with 5 stations, was opened on 3 May 1990 after almost 9 years of construction works. The line opened just before the World Cup. The other 9 stations on Line 3 opened to the southeast in 1991, and northwest to Maciachini Station in 2004.

In March 2005, the Line 2 Abbiategrasso station (south branch from Famagosta) and the Line 1 Rho Fiera station opened. The intermediate station of Pero, on line 1, opened in December 2005. A north extension of Line 3 to Comasina (4 stations) and a new south branch on Line 2 to Assago (2 stations) opened in early 2011.