The '''Extra Deck''' (previously referred to as [[Fusion Deck]]) is a Deck where [[Fusion Monster]]s, [[Synchro Monster]]s, and [[Xyz Monster]]s are stored during a [[Duel]]. They are separate from the [[Main Deck]], and you can search through it to find a Fusion Monster, Synchro Monster, or Xyz Monster that you need. There was is a 15-card limit to the '''Extra Deck''', regardless of how many Fusion Monsters, Synchro Monsters, or Xyz Monsters you include. However, sometime during the 5D's arc the limit became 20, and when the "Numbers" came out the limit was removed completely. The "[[Maximum of 3 Rule]]" for cards of the same name still applies.

If a Fusion Monster, Synchro Monster, or Xyz Monster is on the field, in the [[Graveyard]] or is [[Banishbanish]]ed is returned [[return]]ed to its [[owner]]'s [[hand]] or [[Main Deck|Deck]], it is instead sent to the Extra Deck, since Fusion Monsters, Synchro Monsters, and Xyz Monsters cannot exist in either the [[hand]] or the Main Deck.

Any card or [[card effects effect]]s that still refer to the Fusion Deck now apply to the Extra Deck. Limits on the amount of cards that may be stored in the Extra Deck in the anime and manga have yet to be mentioned.