Skill Gems & Sockets
In Path of Exile, your Skills are not inherent to your character. Instead, you obtain them from Skill Gems that grant you the ability to use an associated Skill. Gems go into Sockets on your armour and weapons, and grant their skills whenever those items are equipped equipped.
For example, to use a Fireball skill in PoE, you'd take the Fireball skill gem, socket it into a matching Blue Socket (more on this in a second) on an item, and equip the item. For as long as that item is equipped, you'll be able to use Fireball, provided you meet other requirements.
The most important detail of this system is the ability to Link gems together. Sockets on an item can be linked, and if they are, you can link a Skill Gem with one or more Support Gems that modify the way your skills work.
Various forms of equipment can come with Sockets. In general, these can be found on:
- One-handed weapons: up to 3.
- Shields: up to 3.
- Two-handed weapons (including Bows): up to 6.
- Helmets, Gloves, and Boots: up to 4.
- Chest Armour: up to 6.
- Quivers, Belts, Rings, Amulets: Usually 0 unless explicitly granted sockets by a modifier.
There are exceptions to these numbers, like a staff limited to 3, but they are rare.
Sockets have Colors, and are usually either Red, Green, or Blue. Colored sockets can only contain gems of the same color, so a red gem can only go in a red socket, a green gem only in a green socket, and so on. White sockets and gems, which are rarer, match any gem or any socket respectively.
In the image at left, for example, the wand has two blue sockets, visible as the blue circles over the wand's icon.
The Attribute requirements of an item affect what color of sockets it prefers to roll: items requiring Strength favor red sockets, items requiring Dexterity favor green sockets, and items requiring Intelligence favor blue sockets. Higher attribute requirements skew the distribution further in favor of matching colors.
It is possible to roll other colors - for example, a piece of Strength-based equipment can have all blue sockets - but large numbers (more than 3 or so) of these so-called 'off-colors' on an item are quite rare.
By themselves, sockets allow you to equip gems. But more important than the existence of sockets are the Links between them. In the image above, for example, the two blue sockets on the Abberath's Horn wand are linked together, indicated by the connection between them.
Any sockets on an item can, in principle, be linked together, but in practice most items you'll find will not be fully linked. They might, for example, have two sockets linked together, a third socket by itself, and then two more sockets linked together. Items with large numbers of links (more than 4) can be valuable, particularly much-sought-after 6-link items (which are always at least moderately valuable and are very rare to find in the wild).
You can reroll the connections between sockets on an item with an Orb of Fusing, discussed in a future section on Currency items. Note, however, that 5- and 6-link items take a very large number of rerolls on average (6-links, for example, take an average of a thousand or so rerolls, and bad streaks of luck can extend that to two or three thousand quite easily).
Active & Support Gems
Skills are provided by Active Skill Gems like Fireball or Heavy Strike. These skills have some effects of their own, but PoE's skill system allows you to modify them further to, for example, increase their damage, add extra projectiles when you use them, or grant you effects when they hit.
This is done through Support Gems. A Support Gem does nothing by itself, or when placed in an unlinked socket - in particular, Support Gems never directly provide any bonus to your character by themselves. However, placing an Active Skill Gem in a socket that is connected by a Link to a Support Gem allows the support to modify the active skill. Mousing over a Support gem will display a list of your active skills, showing which ones it can and cannot modify.
(Players of the Final Fantasy games might recognize this as similar to some of FF's Materia systems.)
For example, you might link the Fireball active skill gem with the Lesser Multiple Projectiles Support gem. This would allow the Lesser Multiple Projectiles gem to apply its effect to the Fireball skill - in this case, reducing the damage of Fireball but causing it to fire two additional Fireball projectiles when used.
Any active skill gem in a chain of links is affected by any support gem in the chain of links (the placement of the gems in the link almost never matters, so order and which gems are next to which other is usually irrelevant). It's possible to link an active skill with up to five support gems if you're fortunate enough to have a six-link item. Linking two Active gems does not affect either of them, in general. Some active gems may give passive bonuses to your character like increases to your damage, but those bonuses are distinct from the effects of support gems and will apply to any skill you use (not just linked ones).
Any class can use any skill gem, although the ones you're given during the early story will depend on your class. All of them will be available to you later on, provided you meet their Attribute requirements.
Gems can be added or removed from sockets at will; they never bind to a socket in a way that is irrecoverable (with the exception of one Unique ring that "eats" support gems). You can right-click to remove a gem from a socket.
Gems do not, in general, need to be placed into specific types of item to work. For example, you do not need to put an Attack gem into a weapon to attack; it could go in your armour just fine. Some items do provide bonuses to gems placed in them (and in those cases, they will specify that those bonuses apply to "socketed gems", meaning gems socketed in that specific item).