The Massachusetts Bay Transit Authority (usually called the MBTA or "the T") is Massachusetts' public transportation system.  

The MBTA opened on September 2, 1897.  Its first line, the Green Line, was the first subway in the Western Hemisphere.  At first, it connected only the Boston Public Garden to Park Street Station - about a half-mile walk.

Today, all together, the parts of the MBTA travel 1392 miles each way, every day.p.3

Parts of the MBTA

The MBTA uses many different forms of public transportation to connect most of the parts of Massachusetts.  As of the MBTA's last official report in 2014, there are 295 different MBTA stations in Massachusetts.p.6

Commuter Rail

The Commuter Rail covers more of Massachusetts than any other part of the MBTA.  The Commuter Rail is a fast train, similar to an Amtrak commuter train.  Of all the MBTA's services, the Commuter Rail runs the farthest from Boston.  Because of this, it is also the most expensive.

In the MBTA's color-coding system, Commuter Rail Trains are purple.

As of 2014, there were a total of 138 Commuter Rail stations in Massachusetts.p.7

All Commuter Rail trains start or finish their journeys at one of two stations in Boston: South Station or North Station.

South Station

Commuter Rail trains run to South Station from towns like:
 Plymouth
 Worcester
 Providence, Rhode Island (including a stop at T.F. Green Airport)

When the New England Patriots are playing at home, the MBTA runs special Commuter Rail trains to Gillette Stadium from both South Station and T.F. Green Airport.

Closer to Boston, Commuter Rail trains stop at a few different Boston neighborhoods on their way to South Station, like Back Bay, Jamaica Plain, Hyde Park, and Dorchester.  

Travelers can change to the MBTA's Red Line subway at South Station.

North Station

Commuter Rail trains run to North Station from towns like:
 Salem
 Gloucester
 Lowell
 Waltham (including a stop at Brandeis University)

Closer to Boston, Commuter Rail trains run through towns near Boston, like Cambridge, Chelsea, Medford, Melrose, and Belmont.

Travelers can change to the MBTA's Green or Orange Lines at North Station.

The Subway
The subway runs mostly in Boston and in the towns next to it.  There are five different subway lines, which are color-coded.  Each line runs to a different part of the city.  There are a total of 66 different subway routes in the Boston area.  The lines cross each other at different points throughout the city so people can switch lines when they need to.  A person does not have to pay to switch from one underground subway to another.

Each train runs in one of two directions: Inbound or Outbound.  If a train is traveling toward Downtown Crossing, it is an Inbound train.  If a train is traveling away from Downtown Crossing, it is an Outbound train.

Orange Line

The Orange Line began running in 1901.  At that time, it was the first public transit in Boston that was elevated (on train tracks above the streets, instead of on the streets or underground).

The Orange Line runs from Malden to Jamaica Plain.  It has 19 stops, including stops at Bunker Hill Community College, Tufts Medical Center, Boston's Chinatown, and Haymarket (a famous outdoor food market).

The Orange Line intersects with every other line on the MBTA.  Travelers can change to any color subway or trolley car from the Orange Line.

Red Line

The Red Line was the last of the four subway lines to be built.

Today, the Red Line runs from Cambridge to inner-city Boston.  Important stops include Harvard Square Station; Kendall/MIT Station; Charles/Massachusetts General Hospital; and JFK/UMASS (the stop for the John F. Kennedy Presidential Library and Museum and the University of Massachusetts Boston.  The Red Line intersects with the Commuter Rail, and with every other subway except the Blue Line.

The Red Line is the most used subway line on the MBTA.  On average, about 74,450,000 people make trips on the Red Line every year.

Blue Line
The Blue Line was built in 1904 as the world's widest underwater streetcar tunnel.  (The Blue Line travels under the Charles River).  By 1924, the Blue Line had been made into a subway.

Today, the Blue Line runs from Revere and East Boston to a small part of downtown Boston.  It stops at Wonderland, which used to be a greyhound racing track; Suffolk Downs, which still is a horse racing track; Revere Beach; Logan Airport; Government Center, where Boston City Hall is located; and the New England Aquarium.  Free shuttle buses take travelers from the Airport MBTA Station to the terminals in the airport.

The Blue Line is used less than any other MBTA subway line.  About 17,880,000 people make trips on the Blue Line every year - about 76% less than the number of people who use the Red Line each year.

Green Line
Part of the green line is a street trolley.  It runs along train tracks in the middle of Boston's streets.  However, some of the Green Line is a subway (underground).  This part of the Green Line goes from Cambridge to downtown Boston.  The Green Line then splits into five different street trolleys that travel to different neighborhoods around Boston.

Longwood Station on the D line, and the Longwood Medical Area Station on the E line, are within walking distance of multiple world-class hospitals, including Brigham and Women's Hospital, Beth Israel Deaconess Medical Center, Dana-Farber Cancer Institute, the Joslin Clinic for Diabetes, and Boston Children's Hospital.

The Green Line is the second most popular subway line on the MBTA.  The Red Line is used a little more often.

Street Trolleys

There are four different street trolleys.  These Green Line trolleys are called the "B," "C," "D," and "E" trains.  There are many trolley stops on the MBTA - 61 in total.p.7

Each train but the "E" train splits off from the underground subway at Kenmore Station.  This is the station closest to Fenway Park, where the Boston Red Sox play.

 The B line runs to Boston College, passing through Boston University
 The C line runs to Cleveland Circle in Brighton
 The D train runs to Newton

The E train splits off from the underground subway at Copley Station.  Its stops include the Prudential Tower, the Boston Symphony Orchestra, Northeastern University, the Boston Museum of Fine Arts.  Its last stop is at the VA Medical Center in Jamaica Plain.  It is the only part of the MBTA that runs on tracks in the middle of the street.

Rapid bus lines

The MBTA has 4 rapid transit bus lines with a total of 30 stops.  These are color-coded silver:

SL1 travels from Logan Airport to South Station, stopping at the federal courthouse, World Trade Center, and each terminal at the airport
SL2 travels from the Boston Design Center to South Station.  It stops at the federal courthouse and the World Trade Center on the way.
SL4 travels from Dudley Station to South Station.  Dudley Station is a major station in Roxbury with connections to 16 different buses.  The SL4's other stops include Tufts Medical Center and Chinatown.
SL5 travels from Dudley Station to Downtown Crossing.  Downtown Crossing is a center of public transit in Boston, with connections to the Red, Orange, and Silver Lines, and 15 different buses.  This is the most popular bus route on the MBTA.  About 14,709 people ride this bus every day.

Commuter Boats

The MBTA also includes commuter boat lines:

 F1 travels from Rowes Wharf in Boston to Hingham Shipyard in Hingham, Massachusetts
 F2H travels from Hingham, to Hull, Massachusetts, to Logan Airport
 F4 travels from Long Wharf in Boston to Charlestown Navy Yard
 At some times of year, a ferry runs from the New England Aquarium to Lynn and Salem

Buses
The MBTA operates 174 different buses.  Together, these buses travel a total of 745 miles, one way, each day.p.e

The two most commonly used buses on the MBTA both average about 14,000 riders every day:
 The 66 bus, which runs from Harvard Square to Dudley Station
 The 39 bus, which runs from Forest Hills (Jamaica Plain) to Back Bay

Summary
This table gives a summary of the different parts of the MBTA:

Criticism

Safety

Some travelers have brought up concerns about safety on the MBTA.  In a 2011 article, Boston Magazine's Jason Schwartz described serious concerns about safety issues on the MBTA - like train fires, and crucial safety issues which he said the MBTA had not addressed.  He wrote: "The system is broke, broken, and about to get a whole lot worse.  No one on Beacon Hill [in the Massachusetts government] wants to address any of this ... History shows that it takes a tragedy - deaths - to fix something as basic as infrastructure.  Hopefully Massachusetts won't wait for that."

In 2014, Robert Murch, a "world-renowned Ouija board" expert, joked that he is more afraid of taking the Red Line than he is of ghosts.

The MBTA has put many programs into place to help prevent crime and terrorism on the MBTA.  The latest report published by the MBTA Transit Police compared crime rates in 2014 and 2015.  Between 2014 and 2015, there was about a 7% increase in crimes on the MBTA.  In 2014, there were 946 reported crimes on the MBTA.  In 2015, there were 1009.  Since over 380,900,000 people ride the MBTA each year, this means that about 0.0003% of travelers were victims of a crime while riding the MBTA in 2015.  Most of these crimes were larceny, robbery, or assault.

Convenience

Some Boston residents have criticized the slowness of the trains, especially the Green Line trolleys.  Kyle Scott Clauss, the author of The Curmudgeon's Guide to the MBTA, writes: "The C branch [of the Green Line] essentially functions as a sort of moving sidewalk leading to and from the Trader Joe's in Coolidge Corner.  It was where Kenyan runner Rita Jeptoo memorably cruised past a Green Line trolley on her way to a first-place finish in the 2014 Boston Marathon."

2015 Blizzards

The MBTA experienced a major crisis in winter of 2015.  This was the snowiest winter in Boston's history, with six weeks of blizzards and heavy snowstorms.  In February alone, 64.8 inches of snow fell in Boston.  The MBTA's train tracks were so frozen and covered with snow that the trains could not drive.  Kyle Scott Clauss of "The Curmudgeon's Guide to the MBTA" joked that "During the Snowpocalpyse of 2015 ... the T's newly installed countdown clocks all read "NOW I AM BECOME DEATH" and workers had to literally set the rails ablaze to keep them from freezing...."

The General Manager of the MBTA, Beverly Scott, shut down all rail service (all trains and trolleys) for over 36 hours.  The MBTA had to hire hundreds of workers to shovel snow and chip ice off the tracks.  On February 11, Scott announced that she would resign from her job, as of April 11, 2015.

References

Public transport
Transport in Massachusetts