There is an extensive transit network in Boston; the "Green line" is characteristic since it contains extensive street running sections.
The 'T' . This is the local subway and train line. It is efficient and cheap and can get you almost anywhere you need to go.
Fast and cheap way from airport to quick visit to city. Follow the Blue Line. Costs $1 on underground area, You can use different subway lines.
The Best way to get around in downtown boston is 'T'
Visit MBTA Web Site for more info.
The 'T' (for tube), the metro. I didn't know it was the first subway in America, did you? It's $1 each ride.