Cities and Knights expands the original Settlers of Catan game by adding in invading barbarian hordes, political gains, and knights to defend the realm, adding a new complexity to a game I'm not sure always needs it. We still play the game with just the Seafarers expansion alone most often, though if you want a much longer, drawn out game with a lot more strategy, then this would do the trick. This game is a staple of my household and friends - the general idea is to place settlements on the intersections of up to three of five types of terrains, and dice rolls cause those terrains to produce resources that you use to build more roads, settlements and cities. The first to reach a certain amount of development wins the game. With Cities and Knights, however, you have a much greater ability to stymie other players, and that tends to slow the game down and introduce a much tighter neck-and-neck race. What's great about this game is the re-play value: every game plays differently, you can randomize the board, the numbers that the terrains produce on, and, obviously, where you place your starting settlements. No one strategy always wins. You do need the original Settlers of Catan game to use this expansion set.