For a detailed description of the interaction between active and support skill gems, see skill gem
To support an active skill, the support gem has to be placed in a socket linked to the socket of the active gem.
Support Skill Gems, more commonly referred to as support gems or just supports are an item class used to augment active skill gems.
They are socketed in the same way as active skill gems, with the difference that they do not give access to another active skill. Instead, they modify any active skill gems in sockets linked to the support gem, while also typically increasing the mana cost of the skill. The modifications vary based on both the active skill being altered and the support gem, and certain skill gem - support gem combinations will leave the skill unmodified. For instance a Module Error: Item link: No results found for search parameter "clarity". gem linked with Module Error: Item link: No results found for search parameter "added fire damage". remains unchanged. Please note that gem tags do not determine the supportability. 
Multiple skill gems may be linked to a support gem, in which case it will modify all of the skills, and multiple support gems may be linked to a skill gem, in which case it will be modified by all of them. However, if two copies of a support gem are linked to the same skill, only the higher level gem will be used. If a body armour contains two copies of a skill gem linked to different sets of support gems, two separate versions of the skill will be available, each with their own modifications. This may be desirable if for instance one version has been modified for single target damage, while another has been modified for area of effect damage. Support Gems add an icon in the form of a coloured letter or symbol to any supported skills' icons on the Skill Bar.
List of support skill gems
- All Support Gems now have Support as part of their name.
- When you hover over a socketed Support Gem, it now shows what Skill Gems it affects by making them glow. The same is true for Skill Gems showing what Support Gems affect them. This currently does not properly handle the case of Support Gems that change a Skill Gem so that it enables or disables other Support Gems.