Types are a means to split monsters into groups (in a broader way to what Attributes do) in order to enable Support Cards granting various effects, to a specific order of monsters. Players use Field Spell Cards to use Type divides to their advantage.
Each monster has 1 Type. There are 22 different legal Types in the TCG and OCG. Divine-Beast is exclusive to the Egyptian Gods and was considered Illegal, although it is now legal in the OCG and will be in TCG as of January (when the first legal English-print God Card is released). Immortal only appears in "Yu-Gi-Oh! The Duelists of the Roses".
??? is used to indicate that a monster's Type is unknown.
Types of Monster Cards
Types of Spell Cards
Types of Trap Cards
Other Types of Card
ATK - DEF - Level - Attribute - Type
Playing Field Zones
Types of Summon
Types of Monster Effects
Types of Effect Monsters
Types of Spell Speed
Aqua - Beast - Beast-Warrior - Dinosaur