See also ../DrivingDirections
General Boston Public Transit Information
Airport to the Summit using the "T" (subway)
With the addition of the Silver Line busses, this has gotten much easier than it used to be. The busses stop at each of the terminals at Logan, and cost $2.00. (Make sure to catch the Silver Line bus to South Station (SL1), not one of the various intra-airport busses. In particular, there is an airport bus that goes to "the subway station", but you don't want to take it, because it goes to a much less convenient station.)
Get off at the Kendall/MIT stop.
Now you'll need to walk two blocks from the Kendall Square station. When you come to the surface, continue down Main Street in the same direction the train was traveling (so as to leave the Marriott Hotel behind you on your right). At the second set of traffic lights you will see the ../StataCenter, on your left. You can't miss it. Really. I mean, you've seen the pictures, right?
Total travel time should be 20-40 minutes depending on how much time you spend waiting for connections.
Arriving in Boston via train or bus
Greyhound buses and most Amtrak trains also arrive at South Station. Follow the signs from the train/bus station to the subway, and board in the Alewife (via Park Street and Harvard) direction, and then follow the directions above.
(Amtrak trains coming from Maine and New Hampshire arrive at North Station, on the Green Line. Take the subway Inbound to Park Street and then follow the directions above, changing to the Red Line, headed outbound towards Alewife)