The Boston area is served by Boston Logan Airport located in East Boston. From the curb outside the baggage claim, you can take the free Silver Line bus to South Station and transfer to the Red Line train in the direction of Alewife. This will bring you to the Harvard Square stop.
If you are arriving in Boston by train or bus, these services often offer South Station as the final destination. This is the most convenient option for an eventual arrival at Harvard Square because it is on the Red Line.
Driving and parking is somewhat difficult in Boston so we recommend that you use public transportation or hired cars if possible.
Here is the official page for the subway (MBTA) if you want to plan additional trips:
If you are driving, there are parking garages in Harvard Square that offer all-day parking. These tend to be expensive ($30 and up). If possible, it is better to use lodgings that offer guest parking and are nearby or offer access to the Red Line.
Here is the city map of parking options:
For those with smartphones, the app “Citymapper” is very helpful for planning trips on public transit and tracking the arrival of trains and buses. The MBTA website also offers this list of other helpful apps.