Cambridge has very good public transportation, with service by both the "T" subway system as well as a number of bus lines. The Red Line of the T connects Cambridge to Boston and a range of other communities in the area. There are also a number of bus lines that run through Cambridge and connect it to other cities and towns. (Source: http://www.tripadvisor.com/Travel-g60890-s303/Cambridge:Massachusetts:Public.Transportation.html)
The rechargeable “CharlieCard” allows you to save money on tickets.
The homepage for public transport in the Greater Boston Area is here.
