As of August 2014, the "Settlers of Catan" board game has four official expansions: "Seafarers," "Cities and Knights," "Traders and Barbarians" and "Explorers and Pirates." In addition, there is an official extension to add up to six players to each game and a pre-2007 adapter kit.
Some of the official expansions can be used in conjunction with the other expansions. They generally include new frame pieces. "Seafarers" includes 15 ships of each color.
Some unofficial expansions, sometimes called "Settlers fan variants," are available but cannot be legally sold. These expansions are generally downloaded from the Internet and include only one or no new pieces.