The Pennsylvania Railroad (reporting mark PRR), legal name as the Pennsylvania Railroad Company, also known as the "Pennsy," was an American Class I railroad that was established in 1846 and headquartered in Philadelphia, Pennsylvania. At its peak in 1882, the Pennsylvania Railroad was the largest railroad (by traffic and revenue), the largest transportation enterprise, and the largest corporation in the world.
Over its existence, Pennsylvania Railroad 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 Railroad (NYC), which carried around three-quarters of the Pennsy's ton-miles.