Railways are much more than just a mode of transport and their impact on the past 200 years of history has been profound. Railways have brought freedom of movement to the masses and been the agents of social change. They have fostered industrial and economic growth, they have been used to mobilise armies and fight wars, and they have inspired great feats of engineering and technological advances. These processes continue today, with the speed of high-speed rail links and growth of urban mass transit systems.

The impact each railway has had in changing the course of history is defined by social, commercial, political, engineering and military influence. Entries range from the Metropolitan Line of the London Underground, the world's first underground railway, to the Central Pacific Railroad, the first transcontinental railway in North America.