The Boston & Maine was the dominant railroad of the New England region of the U.S for a century. It is now part of the Guildford Transportation Industries network.

B&M was first formed beginning in 1835 to create a continuous inland route between the cities of Boston, Massachusetts and Portland, Maine. By 1883, B&M had gained control of other major New England railroads, creating a network of tracks linking Massachusetts and the northern New England states and eastern New York.

B&M flourished with the growth of New England's mill towns in the late 19th and early 20th centuries, but still faced financial struggles. It came under the control of J. P. Morgan around 1910, but anti-trust forces wrested control back. Later it faced heavy debt problems from track construction and costs of acquiring the Fitchburg railroad, causing a reorganization in 1919.

The automobile doomed B&M as a passenger carrier. It gave up on long distance passenger service around 1960 and was able to continue Boston commuter service only by the aid of subsidies from the Massachusetts Bay Transportation Authority.

Beginning in the 1930s, freight business was hurt by the leveling off of New England manufacturing growth and the creation of truck competition.

Bankruptcy came in 1970, leading to the purchase and reorganization of the B&M by Timothy Mellon's Guilford Transportation Industries in 1983.