Path of Exile has three attributes, around which we have placed the character classes. All seven character classes have been announced.
Strength (Red): The Marauder
Strength confers raw brute power, and is represented on weapons by high base damage. Strength armor pieces grant physical damage reduction. Monsters aligned with Strength generally hit hard and take many blows to defeat. Our Strength character class is the Marauder.
Dexterity (Green): The Ranger
Dexterity confers agility in combat, and is represented on weapons by faster attack speeds. Dexterity armor pieces grant the ability to evade enemy blows more often. Monsters aligned with Dexterity are nimble and difficult to hit, often attacking from a distance or with multiple weapons. Our Dexterity character class is the Ranger.
Intelligence (Blue): The Witch
Intelligence confers knowledge – of both arcane magic and deadly combat techniques. It is represented on weapons through improved critical strikes. Intelligence armor pieces grant the wearer a mystical energy shield which protects them from blows and can recharge when they are out of combat. Monsters aligned with intelligence are often weak spell-casters who can be dangerous if not immediately dealt with. Our Intelligence character class is the Witch.
Strength/Dexterity: The Duelist
The Duelist is a hybrid character class that excels at both Strength and Dexterity skills.
Strength/Intelligence: The Templar
The Templar is aligned with both Strength and Intelligence.
Dexterity/Intelligence: The Shadow
The Shadow is aligned with both Dexterity and Intelligence.
Strength/Dexterity/Intelligence: The Scion
The Scion is aligned with all three attributes.
Characters, monsters and items can also be aligned with multiple attributes at once. For example, a staff weapon is generally about 70% strength and 30% intelligence. It differs from a maul (which could be 100% strength) because it is better at scoring critical strikes, but doesn't hit for as much raw physical damage.
There are four playable "hybrid" character classes in Path of Exile: The Duelist, the Templar, the Shadow and the Scion.
Players can use any items or skills, providing they have enough of the relevant attribute requirements. There is the flexibility to dabble in unaligned attributes in order to use off-class skills and items. However, it is generally more efficient for players to invest in the attributes appropriate to their character class.