Throughout the game, players seek to expand their principalities, scoring victory points for certain features.
At the start of the game, each player takes a set of principality cards.
At the diagonals to the settlements lie a total of six resource fields (one in each of the traditional five Catan resources: brick, grain, lumber, ore, wool, and a sixth, gold), the two in the middle being shared by the two settlements.
After this, the player on move may trade resources with their opponent, or with the bank at a ratio of three-to-one, build to expand their settlement, or play cards from their hand.
Improvements typically earn the player commerce points or provide a benefit to the cities and resource fields adjacent to them.
The player with the greatest combined strength value will earn one victory point, while the player with the greatest tournament value will win a free resource if the event die shows "tournament" at the start of their turn.
Defense action cards may be played at any time, while attack and neutral action cards may not be played unless the combined victory point total of both players is at least seven points.
The seven expansions are as follows: Trade and Change introduces road improvements, which are played on top of roads, and region improvements, which may be played above or below a resource field (depending on which side of the principality the resource field is in).
Trade also introduces foreign cards, which are improvements that are to be played in the opposing principality; these may not be voluntarily removed in the expanded game, though there is generally a way for an opponent to remove foreign cards from their principality.
The Trade and Change expanded game limits players to one Counting House (one card is from the base set, the other from the expansion).
Any such units are considered to be part of the metropolis, and metropolises continue to have the benefits of a city.
The Politics and Intrigue expanded game limits players to one Town Hall and one Church (all four cards are from the base set).
Knights and Merchants introduces the pirate fleet, which destroys an opponent's trade or pirate fleet when it is played, as well as give extra resources when the "Year of Plenty" is rolled on the event die.
Knights and Merchants also introduces cards which are only used in the tournament rules, and are omitted from the expanded game.
Science and Progress introduces the cannon, a unit that contributes to strength but not to tournament ratings.
The Science and Progress expanded game limits players to one University (from the expansion).
Wizards also includes new units in dragons, which, like cannons, provide strength but no tournament rating.
Barbarians and Traders introduces two new types of fleets as well as a unit which earns resources when "Tournament" appears on the event die.