In North American railroading terminology, fallen flags are railroads which no longer exist under their original names. At one time, North America was filled with a diverse profusion of small railroad operators which went by a variety of colorful names. Many of these railroads have been lost to time, and are considered fallen flags.

There are two ways in which a railroad can become a fallen flag. In the first sense, a fallen flag is a railroad which has simply ceased to exist because of bankruptcy or the decision to go out of business. As North America shifted from the use of trains to trucks, aircraft, and personal vehicles to move goods and people, many small regional railroads went out of business because no one was using them. In many of these cases, the tracks have been allowed to become defunct in addition to the railroad.

Fallen flags also happen when a railroad stays in business, but loses its name in a merger. Big railroads which buy out smaller companies may retire their names, while larger railroads which merge may come up with a blended name. In the case of a smaller company swallowed up by a big one, it becomes a fallen flag because its name and livery are no longer used. In the case of a big merger, the original corporate names of both railroads are considered to be fallen flags, even though the railroads still exist.

Some railroads have an iconic status in the United States. The Baltimore and Ohio Railroad, known as the B&O, for example, was immortalized in the board game “Monopoly” and became a symbol of American railroading. In 1987, it became a fallen flag when it was acquired by CSX. In the case of iconic fallen flags, some companies have attempted to retain the trade names and livery of smaller railroads they swallowed up, with the goal of ensuring that the names of iconic railroads do not enter the public domain.

Many railroad fans have detailed lists of fallen flags in the United States, along with numerous online tributes. The North American obsession with fallen flags and the history of railroading seems puzzling to many people who are not from this region of the world. The origins of this obsession appear to lie in the vast size of North America, and the fact that trains were a major part of what made Canada and the United States such powerful nations. Furthermore, both Canada and the United States at one point had huge numbers of very small regional railroads to which people became intensely attached because they associated them with specific locales.