A resource is a supply of power or energy used to fuel use of Skills in Diablo games, or occasionally other actions. In the first two games, all characters used Mana as their primary resource, but Diablo III diversified the concept by giving each class its own resource(s) to use, each with different quantities and regeneration rates. Primary resources are shown in orbs in the game's main user interface, the counterpart to Life, together being the two quantities characters must keep a close eye on during gameplay. Resource costs and cooldowns are the primary way skills are balanced, so that powerful skills cannot be over-used and remove the challenge of gameplay.

Depending on classes and skills, other game elements may function as secondary resources in addition to the primary ones, such as charges or stacks of a skill-specific effect, or corpses. Some character builds tend not to go through too many resources, or even any at all, while others may go through cycles of heavy resource use followed by the need to regenerate them. Life itself is sometimes considered the game's foremost resource, as it keeps the player alive but may be sacrificed for the sake of fighting enemies, but in most circumstances it is desirable to keep Life as high as possible at all times, unlike resources designed to be spent.

Maximum resource limits, Resource Cost Reduction, and rate of regeneration of resources are all important character stats in various games, with numerous effects that modify them.

Gold and other items are the resources for the economy aspect of the game, while Greater Rift Keystones and similar tokens are resources for accessing different gameplay elements. However, these are generally known as "currency", "crafting materials", or simply referred to by name, whereas referring to "resources" usually means the combat-oriented gameplay mechanics.

Early games

In Diablo and Diablo II, all classes use Mana as their primary resource. Mana is gained by leveling and further fueled by the Magic or Energy character attributes. Spellcaster classes and builds tend to care more about mana, and have more of it, compared to weapon users. In addition to natural regeneration, plentiful use of potions can keep characters supplied with mana.

Diablo II introduced Stamina as a minor resource.

Diablo Immortal

The resource system is largely absent in Diablo Immortal. The only resources that appear are

• Corpses, used by the Necromancer class to power Corpse Explosion and Corpse Lance skills.
• Anger, used by the Blood Knight class to power the Abomination skill. It regenerates by landing successful attacks on an enemy.
• Primal Power is a resource unique to the Druid class. It fuels transformations and can be used to empower other skills through legendary affixes.

Diablo III

The third game designed different resources for each class. The design of the game's active skills tends to follow a pattern where Primary skills are either free or actually generate resources, while other skills consume them.

• Barbarians use Fury, which decreases naturally when not in combat, but is generated by numerous skills - most only when hitting enemies - as well as by taking damage.
• Crusaders use Wrath, a medium-regenerating resource fueled significantly by primary skills.
• Demon Hunters use two class resources, Hatred and Discipline. Hatred regenerates quickly, is used mostly for combat, and could be thought of as the true primary resource, while Discipline regenerates slowly and is used more for utility. Primary skills generate Hatred, even when not hitting enemies.
• Monks use Spirit, which does not regenerate naturally but is generated by primary skills and several other effects.
• Necromancers use Essence, which similarly to Spirit does not regenerate on its own but can come from skills. Necromancers are the heaviest users of non-traditional resources like corpses and Life, with the most skills that cost no primary resource at all.
• Witch Doctors are the one class that retains the use of Mana from previous games. It regenerates slowly but can be replenished by some skills including passive skills. Primary Skills, known as Signature Spells, can be used for free, although many do not provide mana.
• Wizards use Arcane Power. It regenerates quickly and can be boosted by some skills and items. Wizards have the same Signature Spell concept as Witch Doctors.

Numerous effects, items and Skill Runes change the dynamics of how resources are obtained and used. Of special note is the legendary Aquila Cuirass armor, which grants 50% Damage Reduction as long as the character's current resource supply is above 90%-95% of its maximum.