Public transport in Milan and Lombardy

The public transportation system in Milan includes:
- subway lines;
- suburban rail link, mostly underground (AKA "Passante");
- about 70 surface lines operated with trams and buses.  

The entire network is operated by Azienda Trasporti Milanesi, more commonly known as ATM.
Their website provides complete information on lines, schedules, fares, etc.:
ATM Italian website
ATM English website

The  subway 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. 'Night bus' lines run on Friday and Saturday nights.

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/1811/
A trip on one of those trams is an attraction in and of itself!

Tickets must always be bought before boarding. The standard urban ticket is € 2 and needs to be stamped when boarding.

Also, a public bike sharing service is available: bikeMi