The first expansion to settlers-of-catan. Catan: Seafarers is an expansion to Settlers of Catan. That means it is not a stand-alone game, but supplements Settlers of Catan with additional board pieces (more resource hexes, ocean hexes, frames), tokens (ships and the pirate), and instructions.
The essential difference in game play between Seafarers and Settlers is the addition of shipping routes -- one segment is purchased with one wood and one wool -- allowing expansion onto other islands.
Unlike Settlers, Seafarers comes with rules and instructions for a variety of game scenarios. Whenever applicable, the rules of Settlers of Catan apply in Seafarers.
This tag should be reserved for questions about rules and situations that are specific to Seafarers.