The 4th edition of The Settlers of Catan provides an outer frame that encloses the 19 hexes that make up the island of Catan. The adapter kit provides that frame, the frame extension pieces for the 5-6 player extension, and the harbor pieces that allow you to vary the harbor locations from game to game. This adapter kit also allows you to use the Catan: Seafarers 4th edition with 3rd edition or pre-2007 editions of Settlers.