Rails of Europe is an expansion for Railways of the World. Glenn Drover, one of the two designers of the original game, has designed a European setting for the expansion, which uses the original game's pieces, tiles, money, trains, shares and rules, along with a new map and card deck. There are some rules changed and added for the expansion to reflect the new setting of the expansion.
Due to the complicated corporate history of Eagle Games, this expansion was unusual - it was originally an official, yet unlicensed expansion of Railroad Tycoon. It was official, since the designer of the original game also designed this expansion and it was to be published by a company that is a descendant (of sorts) of Eagle Games. The expansion is unlicensed because it never bore the Railroad Tycoon name, which was licensed from Sid Meier's computer game. Its status as an expansion of Railways of the World is much more official, although it existed before the base game of Railways of the World was published.