The 2021 edition of Citadels features the same great content included in the 2016 edition of the game, but is scaled down to fit a smaller, more portable box.

In Citadels, players take on roles of characters they hire in order to help them acquire gold and erect buildings. The game ends at the close of a round when a player erects their eighth building. Players then count their points, and the player with the most points wins. Players begin the game with a number of building cards in their hand; buildings come in five colors, with the purple buildings typically having a special ability and the other colored buildings providing a benefit when you play certain characters.

At the beginning of each round, the player who was king the previous round discards one of the eight character cards at random, selects one, then passes the cards to the next player, etc. until each player has secretly picked a character. Each character has a special ability, and the functionality of any character depends upon your situation, and that of your opponents. The characters then perform their actions in numerical order: the assassin eliminating another character for the round, the thief stealing gold from another character, the wizard switching building cards with another player, the warlord optionally destroys a building in play, and so on. On a turn, a player gains two or more gold (or pulls two building cards then discards one), then optionally constructs one building (or up to three if playing the architect this round). Buildings cost gold equal to the number of symbols on them, and each building is worth a set number of points. In addition to points from buildings, at the end of the game a player earns bonus points for having eight buildings or buildings of all five colors.