The Game Mat helps you organize your cards during a Duel. When you use your cards you place them on the Game Mat. Different kinds of cards are placed in different Zones. Each Duelist needs their own Game Mat; place them together while Dueling. This combined space is known as the field The Game Mat contained in this product is just for your half of the field. The cards you "control" are the cards on your side of the field. You can also Duel without using the Game Mat as long as you remember where to place the cards. This is where you put your monsters when they're played.