largest of the New England railroads, operating in central and northern Massachusetts, southeastern Maine, and New Hampshire, with a few miles in Vermont and New York. The Boston and Maine's earliest predecessor was the Andover and Wilmington Railroad, which was chartered in 1833. The railroad's first section of track, running east from Wilmington, Mass., opened in 1836, and the railroad adopted the name Boston & Portland Railroad in 1839. Another major predecessor, the Boston & Maine Railroad, was incorporated in 1835 and merged with the Boston & Portland in 1841 to form the Boston and Maine Railroad Company.

Ultimately 111 companies were absorbed into the Boston and Maine, which connects New England with other rail lines serving regions to the south and west. The 4.75-mile (7.6-kilometre) Hoosac Tunnel, acquired along with the Fitchburg Railroad, was built in 1851–75 through the Berkshire Hills of Massachusetts, occasioning the first use of pneumatic drills in the United States. At the time it was completed in 1875, the Hoosac Tunnel was the longest rock tunnel in the United States.

Although the Boston and Maine Railroad went bankrupt in the 1970s, it continued to operate 1,416 miles (2,278 km) of main and branch lines while undergoing reorganization. It derived its largest sources of freight revenue from the transport of paper, petroleum and coal, and food and grain-mill products. The Boston and Maine sold 279 miles (449 km) of its commuter lines to the Massachusetts Bay Transportation Authority in the 1970s. In 1984 the railroad was bought by Guilford Transportation Industries, whose owner, Timothy Mellon, was the great-grandson of the financier Andrew Mellon.