Traders & Barbarians is the third major expansion for The Settlers of Catan. It is actually a compilation of small expansions and variants. (It is independent of the Seafarers and Cities & Knights expansions, but can be combined with them.)
Well-tried variants such as “Catan Event Cards,” “Harbormaster,” and “Catan for Two” offer alternatives for customizing the game to your own needs. In addition, the 2-player variant allows you to play the Base Game as well as all scenarios of this expansion against only one opponent.