Board space refers to the number of available slots for cards to remain in play at a time. There are three areas where cards can remain in play: the board, where minions exist; the hero portrait, where certain spells exist; and the weapon slot (opposite to the Hero Power), where weapons exist.
- Cards that summon "all" of something, such as or , will only summon until that respective part of the board is full.
- Minions cannot be played from hand when a player's board is full, nor can spells that merely summon minions.
- Spells that summon minions in addition to other effects can be played.
- If a minion would be summoned but the board is full, nothing happens. It will neither enter play nor be destroyed.
- Using a Mind control effect such as , , or when you have a full board kills the minion instead of taking it. Playing a mind control spell with six minions on your board, one of which summons a minion "whenever you cast a spell," such as , causes the triggered friendly minion to summon a minion, after which the enemy minion targeted by your spell dies.
- A magnetic minion cannot be magnetized to another minion on a full board.
- Minions can appear to occupy more than seven spaces while processing long animations, such as multiple Shudderwocks with summoning Battlecries played quickly in the same turn. This is purely visual - any extra minions are not actually in play yet and cannot be affected by any cards.
- Only one of each unique spell can be in play at a time. You will be unable to play any duplicate cards.
- Only one Quest is allowed in play at a time.
- Equipping a weapon while you have one equipped already will destroy the currently-equipped weapon, triggering its Deathrattle and replacing it with the newly played card.