The Main Deck is the "main" deck, the one a duelist would regularly use. It can contain up to 60 cards, with the min. being 40. The Side Deck is a deck often used for Matches (3 Duels in a row) which can replace cards in the Main Deck during the break between duels. Finally, the Extra Deck (Before the Synchros were released, formerly known as the Fusion Deck) is a Deck where the Fusion and Synchro Monsters reside. Both the side and Extra decks can contain up to 15 cards.