Navigation on city streets is very hard if you're not familiar with the area. Driving is to be avoided if possible. There are many one-way streets, usually arranged haphazardly and poorly marked for drivers. Signage is nothing short of terrible and often you will have no clue what street you are crossing. Due to constant construction, the correct directions one day could be entirely wrong the next. Parking is expensive, and traffic can be slow - watch out for lots of double-parked vehicles. Drivers are also notorious for being aggressive, as are pedestrians and bicyclists, somewhat. Especially avoid driving during rush hour on weekdays; streets and highways become extremely crowded. For the most part, highways are clear outside of rush hour. The recent opening of the Central Artery Tunnel means that traffic on I-93 through downtown and to the airport via the Ted Williams Tunnel (I-90) are particularly quick, though confusingly signed.

For most tourist destinations in Boston and Cambridge, it's usually advisable to leave your car behind and take the subway. You'll do a bit more walking, but that will give you a chance to see the sights. However, much of the parking in Boston and surrounding towns is limited to neighborhood residents, who have stickers identifying their cars. You should therefore check whether parking on a particular street is open to you, and consider using metered parking or public or private lots.

Parking
If you're looking for a place to park in the city, the Boston Common Garage is a good choice. There are three levels of parking under The Common. The garage is very clean and its central location makes it a good starting point for a day trip in the city. To get in and out of the garage, there are four pavilions on The Common; each has stairs and an elevator. Once out of the garage, the Park Street and Boylston Street subway stops are only a two or three minute walk away.

Public transit
Public transit in Boston is convenient and relatively inexpensive, and can take you directly to most points of interest. A single public transit agency serves the Boston Metro area, the Massachusetts Bay Transportation Authority ("MBTA", or "the T" for short). The MBTA is the fourth-largest transit system in the U.S. For complete schedules, maps, and other information, see their official website.

The T consists of several components: subway, bus, water shuttles, and commuter rail. The subway is composed of four color-coded light rail lines: orange, red, blue, and green. The Red and Orange lines travel generally north-south; the Blue and Green lines travel generally east-west. The Green Line splits into four branches going west and are known as the B, C, D and E lines; the Red Line splits in two directions going south and are known as the Braintree and Ashmont branches, the latter of which connects to a streetcar line to Mattapan. Going west on the Green Line, the E line branches off at Copley Square station, the other three split at Kenmore Square station. Going south, the Red Line splits at JFK/UMass station. Subway maps usually also include the Commuter Rail (long-distance heavy rail) which is color-coded purple, and the Silver Line, a Bus Rapid Transit (BRT) line currently under expansion. Collectively, the light rail and Silver Lines are known as Rapid Transit, and they all converge downtown.

The subway system is slightly confusing in that directions are often marked "inbound" and "outbound", rather than with a destination. "Inbound" means "into the center of Boston", where all four lines converge at four stops: State (Blue and Orange), Park Street (Red and Green), Government Center (Blue and Green), and Downtown Crossing (Orange and Red). "Outbound" means "away from the center of Boston". Of course, once one is in the center, the lines may indicate the actual destination of the trains, because all directions are "outbound". Nevertheless, note that the four stations listed above surround the center; for example, travel from Park Street to Government Center on the Green Line would be Inbound. One of the better ways to determine which way to go is to note what the last stop of the train is (usually denoted on the subway platform maps). For example, a train going outbound to Alewife from Downtown Crossing, is going to stop at all stops in between these two stations.

Note that subway and light rail service generally stops between midnight and 2am. Each line (green, blue, etc.) has a "last train" time, starting at one end of the line and going to the other. For example, Alewife, the north end of the red line, has a last train leaving at 1:15 am, which means it'll most likely arrive at Park St. going south between 1:35 and 2, depending on the number of people using the T that night. Therefore, make sure to check with a T employee (usually someone is available in one of the token booths by the turnstiles) or with a bus driver to get the "last train" time for the subway or bus line you want to take.

You may have heard of the Night Owl, a bus service that ran the same route as the subways and some bus lines, which ran at later times at night, but it has been discontinued.

Your current alternative to late-night public transit is a taxi - expect to spend at least $5 and possibly up to $30 in the immediate surroundings (this includes the initial fare, a small tip for the driver, small one-way streets, bad traffic, construction, tolls for bridges, tolls for tunnels, tolls for the MassPike, and any wait time). To get further out of Boston, expect to spend much more (for example, from the airport to Wellesley, a Boston suburb, would be around $80, which includes the actual driving and tolls along the way).

Unlimited-ride subway and bus passes are available from the T. If you're going to be riding a lot around town, these are worth investigating. See the MBTA for complete fare information on tourist passes. You should be aware that the Visitor pass is $35 for 7 days, whilst the Combo pass is just $16.50 for 7 days, and they are more or less the same. The Combo pass is the one to get.

The cost of a single ride on the T is $1.25. Buy a token from the booth to go through the turnstiles. This will get you to most destinations, although if you are going to the outskirts of Boston (specifically, Newton or Braintree), an extra charge may apply. You should get two tokens if you are planning a return trip as there can sometimes be long lines at the token booth. Parking at the Alewife station on the Red line is ample but will cost you $4.50 no matter when you come and go (for each 24 hour period).

Bikes are allowed on all MBTA vehicles EXCEPT buses. Please note there are certain rules you have to follow, so make sure you check their website. There are also public ferries available, but some may be through private companies, so be sure to check the fares at the companies' websites.

Important note: Many subway stations do not accept credit cards and don't have ATMs, so bring cash. Between the fall of 2005 and 2006, the MBTA will be launching the Charlie Card and Charlie Ticket service that will replace the tokens. You'll be able to use a credit card for these.

By foot
Boston is a very compact city, given that walking was the predominant form of transportation for most of the city's history. Most of the major attractions can be visited on foot, although the climate is rather cold from December to April. Within intersections (or at any convenient point along the street), mob rule is generally observed, and pedestrians rarely wait for the "walk" signal. Be careful when crossing the streets.