Monster Zones (モンスターゾーン Monsutāzōn), formerly Monster Card Zones (モンスターカードゾーン Monsutākādozōn), are the Zones where monsters are placed on the field. In the OCG, there are two types of Monster Zones: Main Monster Zones and Extra Monster Zones.
Cards on the field are treated as monsters if and only if they are in a Monster Zone. Monster Cards on the field are not treated as monsters if they are in other Zones (such as the Spell & Trap Zone). Likewise, Spell and Trap Cards in the Monster Zones are treated as monsters (although Trap Monsters are treated as Trap Cards as well, so they also require a Spell & Trap Zone but are placed in the Monster Zone). Xyz Materials are not considered to be in a Monster Zone.
A monster cannot be Summoned unless there is an appropriate Monster Zone to Summon that monster in, unless performing its Summon would cause an appropriate Monster Zone to become available. For example, even if all of a player's Main Monster Zones are occupied, that player can still Tribute Summon a monster to their field as long as they Tribute at least one monster in their Main Monster Zones. Even if the opponent controls monsters in both Extra Monster Zones due to achieving an Extra Link, the player can still Summon a monster to an Extra Monster Zone as long as one of the Extra Monster Zones becomes available when performing the Summon (such as by using a monster in one of these Zones as Material).
If control of a monster is changed or a temporarily banished monster returns to the field, it is placed in its controller's Main Monster Zone (regardless of its original Zone). If there is no available Main Monster Zone, that monster is sent to the Graveyard
The player who performs the Summon or Set, regardless of who will control the Summoned monster, decides which Monster Zone the Summoned/Set monster is placed in. The Zone into which a monster will be Summoned/Set is decided before the Summon negation window. A monster Summoned/Set from anywhere other than the Extra Deck can be Summoned/Set in any unoccupied Main Monster Zone on the appropriate player's field (unless the Zone has been rendered unusable by a card like "Ojama King"); a monster Summoned from the Extra Deck can be Summoned in any unoccupied Linked Zone on the appropriate player's field or either Extra Monster Zone (as long as the Summon would not result in a player controlling monsters in both Extra Monster Zones, unless this Summon achieves an Extra Link).
Monsters cannot be moved between Zones, except by a card effect like "Senet Switch".
On game mats, Main Monster Zones are located in the upper-middle and are often colored brown. On OCG game mats, Extra Monster Zones are located in the center of the field and are colored green.
- ↑ "Master Rule 3 Overview". Konami. http://www.yugioh-card.com/hk/howto/master_rule_3.php?lang=cn-t.