The Pennsylvania Railroad (reporting mark PRR, legal name The Pennsylvania Railroad Company, also known as the "Pennsy") was an American Class I railroad that was established in 1846 and was headquartered in Philadelphia, Pennsylvania. It was so named because it was established in the Commonwealth of Pennsylvania.

By 1882, the Pennsylvania Railroad had become the largest railroad (by traffic and revenue), the largest transportation enterprise, and the largest corporation in the world. Its budget was second only to the U.S. government. The corporation still holds the record for the longest continuous dividend history: it paid out annual dividends to shareholders for more than 100 consecutive years.Over the years, it acquired, merged with or owned part of at least 800 other rail lines and companies. At the end of 1926, it operated 11,640.66 miles (18,733.83 kilometers) of rail line; in the 1920s, it carried nearly three times the traffic as other railroads of comparable length, such as the Union Pacific and Atchison, Topeka & Santa Fe railroads. Its only formidable rival was the New York Central (NYC), which carried around three-quarters of the Pennsy's ton-miles.

In 1968, the Pennsylvania Railroad merged with its rival New York Central Railroad and the railroad eventually went by the name of Penn Central Transportation Company, or "Penn Central" for short. The former competitors networks integrated poorly with each other, and the railroad filed for bankruptcy within two years.:Chapter 1Bankruptcy continued and on April 1, 1976, the railroad gave up its railroad assets, along with the assets of several other failing northeastern railroads, to a new railroad named Consolidated Rail Corporation, or Conrail for short. Conrail was itself purchased and split up in 1999 with 58 percent of the system going to the Norfolk Southern Railway (NS), including nearly all of the remaining former Pennsylvania Railroad. US passenger carrier Amtrak received the electrified segment of the Main Line east of Harrisburg.

After 1976, the railroad eventually became an insurance company and now goes by the name of American Premier Underwriters and is now a subsidiary of American Financial Group.

The New York Central Railroad (reporting mark NYC) was a railroad primarily operating in the Great Lakes and Mid-Atlantic regions of the United States. The railroad primarily connected greater New York and Boston in the east with Chicago and St. Louis in the Midwest, along with the intermediate cities of Albany, Buffalo, Cleveland, Cincinnati, Detroit, and Syracuse. New York Central was headquartered in New York City's New York Central Building, adjacent to its largest station, Grand Central Terminal.

The railroad was established in 1853, consolidating several existing railroad companies. In 1968, the NYC merged with its former rival, the Pennsylvania Railroad, to form Penn Central. Penn Central went bankrupt in 1970 and merged into Conrail in 1976. Conrail was broken-up in 1999, and portions of its system were transferred to CSX and Norfolk Southern Railway, with CSX acquiring most of the old New York Central trackage.

Extensive trackage existed in the states of New York, Pennsylvania, Ohio, Michigan, Indiana, Illinois, Massachusetts and West Virginia, plus additional trackage in the Canadian provinces of Ontario (Southwestern and Eastern Ontario) and Quebec (South of Montreal). At the end of 1925, the NYC operated 11,584 miles (18,643 km) of road and 26,395 miles (42,479 km) of track; at the end of 1967 the mileages were 9,696 miles (15,604 km) and 18,454 miles (29,699 km).