Public transportation in Milan is excellent, and is therefore the preferred method of getting around Milan.  

The public transportation system includes:

- four underground/subway lines (#1 - red, #2 - green, #3 - yellow, #5 - purple );

- one (mostly underground) suburban rail link (AKA "Passante", drawn in blue on subway maps);

- about 70 surface lines operated with trams, trolleys, and buses.  

Extensions to #1 and #5 underground lines are currently (2014) under construction; also, works on a fifth subway line (#4 - light blue) have started in 2012 (completion expected in 2018).  This new line will reach out to Linate airport, East of the city center.

The entire network is operated by Azienda Trasporti Milanesi, more commonly known as ATM (http://www.atm.it ).  The suburban rail system is operated by Trenord, but ATM city tickets can be used on trains  within the city limits.

The ATM website has complete information on lines, schedules, fares, etc., and has an English version.

In 2011, ATM has published a map of central Milan with all public transport lines, which can be downloaded from http://www.atm-mi.it/it/ViaggiaConNoi...  An updated map of the underground system is available at http://www.atm-mi.it/it/ViaggiaConNoi...

The metro operates roughly from 6 AM to midnight every day (lines #1, 2, and 3 are operated by bus throughout the night 7 days a week). Trams and buses start about an hour earlier and run until an hour or so later, #90 and 91 buses operate 24 hours a day, 7 days a week. Additionally, several 'night bus' lines run on Friday and Saturday nights. Check www.atm.it for complete timetables.

A few tram lines (including #1, which runs through most of the city center and  near the central train station) are still operated with vintage trams built in the 1920's -- ten of those vehicles were shipped to the USA and are now in use on San Francisco's 'F' streetcar line -- http://www.streetcar.org/streetcars/1.... A trip on one of those trams is an attraction in and of itself!

For transport from and to Milan airports please check "arriving and departing" article. 

To find out connections throughout the Lombardy region (bus, rail, etc..), check the Lombardy regional government's journey planner: site.

Tickets (including daily passes and cumulative tickets) must always be bought before boarding, and must always be promptly stamped in the little red machine every time you board a bus or tram, or at subway turnstiles. There are frequent inspections, and since inspectors move in flocks it is impossible to escape.  It's best to go by the book and avoid a large fine (and a ''brutta figura'')!

Urban tickets (i.e. valid within city limits) are relatively inexpensive. The standard ticket is € 1.50.  This is valid 90 minutes from stamping for unlimited rides on surface transport, and/or one subway or suburban train ride.  There are also 24-hour passes (€ 4.50) and 48-hour passes (€ 8.25), which are good value if you plan to use public transport extensively. For more details: ATM ticket fare. Note: all children under 6 travel free.  Up to 2 children between 6 and 10 accompanied by an adult travel free as well (proof of age required).  Passes and tickets are available from most newspaper stands and tobacconists, or from multilingual, touchscreen vending machines at all subway stops (these also take credit cards).  ATM  also has a ticket office at the Duomo subway stop. 

Cumulative tickets will let you travel between Milan  and the towns in the greater Milan area (this zone-based pricing system is known as SITAM ). For tickets to Rho Fiera Milano see this page. These cumulative tickets are not valid on trains outside Milan, they only include urban rail lines operated by Trenord and the "Passante ferroviario" (suburban rail link) inside Milan. To view routes use the ATM journey planner.

Integrated travel cards known as 'Io viaggio Ovunque in Lombardia' can be used on every public transport service throughout the Lombardia region (including first class regional trains but excluding the Malpensa Express). These area available for 1, 2, 3 or 7 consecutive days. Fares: one day 15 €; two days 25 €; three days 30 €; seven days 40 €.

Note: all children under 14 travel free on public transport in Lombardy when accompanied by a family member holding a valid ticket or pass. The reduction is granted simply filling out the form that can be downloaded from the Forms section "I travel with family" of Lombardy region and also available in the main ticket offices, information points and websites of transport companies. The declaration, duly completed, enables kids to meet the requirements to travel on public transport for free. It is valid for 60 days, after which it must be renewed. Delivering the statement to one of the transport company offices, along with two passport photos and a copy of the children ID card, you will receive the free  "I travel with family" card for the children. The card is personal and includes a list of regional operators that will let the young travel free of charge. 

For children under 18, save 20% on the second subscription and subscription free from the third onwards.  Also in this case a form has to be filled out.