The Supply consists of all the cards a player is able to buy in a game. These include the Kingdom cards, the basic Treasure and Victory cards, Curses, and Ruins if they are available. Some cards, such as Prizes, Spoils, Madman, and Mercenary, are not in the Supply, but are able to be gained or otherwise acquired through the effects of specific other cards.
A normal game of Dominion has a Supply consisting of Estates, Duchies, Provinces, Copper, Silver, Gold, Curses, and 10 piles of Kingdom cards (which are usually, but not always, Actions). Some expansions add to the Supply:
- Alchemy adds Potions when -costing cards are in the Kingdom.
- Prosperity can add Colonies and Platinum.
- Young Witch, from Cornucopia, adds an 11th Kingdom card as its Bane.
- Looters, from Dark Ages, add Ruins when they are present.
Ordinarily each pile in the Supply consists of several copies of the same card. The three exceptions to this are Ruins, Knights, and Split pile cards, which are each Supply piles containing more than one differently named cards; in these cases, only the top card of the pile is visible to players and available to be bought or gained. For this reason, although the entirety of any Supply pile is physically part of the Supply, only the top card of any pile is considered to be "in the Supply". For instance, when Band of Misfits requires you to choose a "card in the Supply", you may not choose a card in the Ruins or Knights pile other than the one on top.
When a pile is empty, it is no longer considered to be part of the Supply. Should it cease to be empty, such as through Ambassador, it would once again be part of the Supply. A player can always check how many cards are left in any Supply pile, as well as any non-Supply pile.
When you choose a card to buy or gain, unless otherwise instructed, you must choose a card in the Supply.
 Cards that reference the Supply
 Cards that trash from the Supply
 Cards that emulate a card in the Supply
 Cards that care about empty Supply piles
 Cards that pick a pile in the Supply
 Cards that interact with multiple Supply piles at setup
Anything that is not from a Basic card pile or a Kingdom card pile is not considered to be part of the Supply.
 Cards not in the Supply
There are many cards available in Dominion that can never actually be bought; these are marked with an asterisked cost, and an italicized parenthetical at the bottom of their card text explaining that they are not in the Supply. The asterisk in their cost has no effect on gameplay other than to signify this; all effects that care about costs affect non-Supply cards normally. Non-Supply cards must be gained (or otherwise acquired) via other cards that are available in the Supply, namely:
- Tournament instructs you to gain a Prize from the Prize pile.
- Bandit Camp, Marauder, and Pillage instruct you to gain a Spoils from the Spoils pile.
- Hermit instructs you to gain a Madman from the Madman pile.
- Urchin instructs you to gain a Mercenary from the Mercenary pile.
- Page and Peasant each exchange into a number of increasingly more powerful cards.
- Vampire exchanges for a Bat from the Bat pile.
- Leprechaun and Magic Lamp instruct you to gain a Wish (or three Wishes, in the case of Magic Lamp) from the Wish pile.
- Haunted Mirror instructs you to gain a Ghost from the Ghost pile.
- Devil's Workshop and Tormentor instruct you to gain an Imp from the Imp pile.
- The Swamp's Gift instructs you to gain a Will-o'-Wisp from the Will-o'-Wisp pile.
- Exorcist instructs you to gain any Spirit (one of Will-o'-Wisp, Imp, or Ghost) from its appropriate pile.
Additionally, while Shelters, Heirlooms, and Zombies do not have an asterisked cost, and do not have card text distinguishing them as such, they are not part of the Supply, as they do not come from a pile.
Technically, the trash is not part of the Supply. While the cards in it can come originally from the Supply, you cannot normally buy or gain from the trash. There are a few cards that allow you to gain from it, however:
- Lurker, Graverobber and Rogue enable you to gain a card of your choice from the trash (subject to certain restrictions).
- Thief and Noble Brigand instruct you to gain specific cards which were just trashed.
- Black Market tells you to buy from the Black Market deck, which is constructed from Kingdom cards not available in the current game's Supply.
- Events can be bought during a player's normal Buy phase, but given that they cannot, by their nature, be gained, are not truly part of the Supply.
- Landmarks, though represented by cards on the table along with the Supply, are really just new rules that apply for that particular game.