From Logan Airport 

If you are arriving to Cambridge via Boston's Logan Airport, you can choose between taking a taxi or the MBTA, Boston's public transportation system. There is a taxi queue outside each baggage claim. While the lines may appear long at times, the taxis are readily available and the wait is usually short. If your destination is not a major hotel, it is best to have directions with you, as many Boston taxis are not familiar with the Cambridge neighborhood streets. Traffic is the main wildcard in estimating your travel time.

Via the subway, the trip will take between 30-45 minutes, depending on which subway stop is closest to your Cambridge destination. From baggage claim, follow the signs to Boston's newest subway line, the Silver Line. The buses run approximately every 10 minutes. Take the Silver Line to the end, South Station. At South Station, follow the signs to transfer to the Red Line. There are 4 Red Line stops in Cambridge - Kendall, Central, Harvard and Porter. Consult your destination to determine which will be closest.

From South Station

Arriving to Cambridge via bus or train is similar to the commute from Logan Airport. There are taxis readily available outside the terminal and the subway is a straight shot on the Red Line, as described above.

Driving

Depending on what part of Cambridge is your destination, you'll find Cambridge easily accessible from major highways such as I-93 and I-90  and the bordering throughways of Memorial Drive, Alewife Brook Parkway, McGrath O'Brien Highway and Route 2. Getting detailed directions in advance of your trip is strongly recommended, as Cambridge is not a grid city. There are many rotaries and one-way streets that can make driving to/from Cambridge and adventure, to say the least.