In Duel Masters, all decks must follow these simple rules:

• In the TCG, all decks must have at least 40 cards in it. However, it is often recommended to have the minimum 40. A deck in the OCG is limited to exactly 40 cards.
• Your deck can contain up to 4 copies of any card in your deck, except for cards featured on the Hall of Fame. A card that uses a different artwork from a different set such as Spiral Gate still counts as the same card.
• You may have up to 8 psychic creatures in your hyperspatial zone. You may have up to 4 copies of any particular psychic creature in your hyperspatial zone.

During the game, unless a card says otherwise, neither you nor your opponent can look at the cards in your deck or change their order.