If you are coming from the East Coast, you can take an Amtrak train
to South Station or Back Bay Station from most major cities and towns that are south of Boston. North Station serves points north. However, fares tend to be on the expensive side, and Amtrak is notorious for delays and inefficiency. Bear in mind, 3-day advance purchase on the Web will yield Amtrak discount fares that you will never see at the walk-up window. Unfortunately, the political will for the "Big Dig", Boston's monumental highway submersion project, didn't include extending the railroad through Boston -- e.g., there isn't a straight shot from New York to Portland.
Several long-haul bus lines offer service to Boston. Of course, the closer you live to Boston, the easier it is to find a convenient option. The Hampton Jitney serves Long Island, Fung Wah, Sunshine Travel, and Lucky Star busses offer cheap frequent service from New York City to Boston (Chinatown to Chinatown), and Greyhound and Peter Pan serve the East Coast and beyond. Most buses drop you off at South Station, where you can catch the Red Line and Silver Line "T", or some commuter trains. At the higher end, a recent start-up, LimoLiner, operates vans between Boston and NY downtowns with airplane-type seats, internet connections and attendants. With Boston's huge student population, trains and buses can be crowded, especially during holidays, Fridays, Saturdays and Sundays, so try to reserve a seat ahead of time.
The cheapest way from and to the airport - short of having a friend picking you up - is Boston's subway and trolley system, known as the "T" (Massachusetts Bay Transportation Authority
, also the "MTA" of folk song fame). The "T" shares North Station, South Station, and Back Bay Station with commuter rail, as well as AMTRAK
. It also shares the city's major bus depot at South Station. Here, "shares" means "under one roof'.