In Feudalia, you control three feuds, with one small village included in each feud. A small population of vassals work in those feuds and provide you with resources or earn you money, with both of those things being necessary to make your small village grow, increase your population, specialize your vassals, and hire great masters.
Apart from trying to have the most prosperous feuds, you must help construct the cathedral that the king demands for his own sake and glory. In addition to this demand, the tax collector will pressure you for funds, and you must constantly worry about possible attacks from neighboring feudal lords, although negotiation might help you achieve your objectives despite these potential setbacks.
In more detail, each turn you draw five cards from your vassals' deck. If you get the tax collector, you must play it first and pay half the resources in each of your feuds (or in the case you cannot pay anything, half your profits in hand). There are many actions you can do, as many times as you want and whatever order you want, with all the remaining cards in your hand and with the great masters in your feuds.
Feudalia can end different ways depending on the desires of the players. A typical game would be played until 10 points, with players earning points by evolving their feuds and constructing the cathedral. For a tenser endgame, 12 points is the right spot to end. Another possibility is to play until the cathedral is built, but this ending makes for longer games.
Feudalia includes a one-player mode designed as a training ground for games with 2-4 players, which keeps the same rules no matter the number of players.