Mana

Mana is the most common resource heroes use to cast abilities. Underneath your green Health bar a blue bar shows your Hero's Mana supply. Using an ability requires you to have enough Mana to fulfill it's Mana cost. If a Hero starts running low of Mana, the number of Abilities he/she is able to use immediately drops (they’ll turn dark purple in the Hero’s Ability list). Mana replenishes over time, but not always quickly.

Scaling
Heroes that use Mana start the game with 500 Mana at level 1 and gain 10 maximum Mana every level onwards. What this means is by level 20 mana users have a mana pool that is almost 40% larger and have over 60% more mana regeneration. Mana costs are constant, so as the game progresses mana becomes less and less of an issue. Some heroes can additionally increase their Mana cap through Talents.

Mana Regeneration
A hero's Mana restores over time based on their Mana Regeneneration. Mana regen is passive and continues even when a hero is disabled. Mana regen is measured in mana per second. Mana regen can be increased by some talents. Heroes that use mana, except for Gul'dan and Probius, start with 3 mana per second at level 1 and gain .0975 mana per second every level. There are also some abilities that can refund Mana if their requirement is fulfilled (e.g. Medivh's "Arcane Rift" refunds some of the Mana cost if it hits a hero).

Other Resources
Some heroes don't use Mana at all or use another resource similar to Mana. Heroes that do not use Mana include Abathur, Auriel, Chen, Cho'gall, Deathwing, D.Va, Fenix, Gazlowe, Hogger, Illidan, Junkrat, Lt. Morales, The Lost Vikings, Murky, Samuro, Sonya, Tracer, Valeera, and Zarya.

Core Concept

 * Mana is a limiting factor for self-sustain: Any hero who can use abilities to recover their own Health quickly, without taking risks, is generally be limited by Mana. This helps ensure that damage enemies deal to them actually matters and isn't just magically erased at no cost. Requiring Mana for HP sustain makes it possible to win wars of attrition and is one way to keep game length from spiraling out of control. Heroes who don't require Mana for sustain generally "pay" for their sustain in other ways (such as Auriel who relies on aggression to generate Energy), or have more modestly-paced sustain with adequate counterplay (such as Muradin, Illidan, Sonya).
 * Mana is a limiting factor for harassment: Ranged Assasins with harassment abilities, like Li-Ming, Jaina, Kael'thas, can wear down enemies before committing to a fight. At the same time, those abilities are packaged with significant Mana costs and/or Cooldowns that really give them weight - the cost of missing is not trivial, so it feels really good when you hit. It's important that something limits the frequency with which those abilities are used, and that enemies feel like dodging those abilities is meaningful.
 * Mana can be a very flexible resource:' Used properly, Mana forces you to think about your ability use in more of a long-term perspective beyond just "spam on CD". It can also serve as a limiter in cases where Cooldowns don't really factor in, such as Li-Ming's trait reset rampages. Interestingly, the degree to which Li-Ming burns her Mana before resets kick in ends up affecting how crazy she can go with those resets, so how you choose to spend your resources in that case has a big impact.
 * Mana should be a meaningful part of the game, particularly in the early stages when wave clear is at a higher premium. As the game progresses, Mana tension should become less important as Heroes gain more base Mana and the game’s focus shifts to team fighting.

Refill Mana

 * A Regeneration Globe will heal 9% of the Heroes maximum Health and 7% of the Heroes maximum Mana in 5 ticks over 5 seconds.
 * A Healing Fountain will regenerate 30% of the Heroes maximum Mana over a period of 20 seconds.
 * The Hearthstone (hotkey: B.) allows heroes to teleport to their Hall of Storms after channeling for 6 seconds. Upon completion, the hero is healed for 1125 health, 150 mana.
 * Within the Hall of Storms Health and mana are restored by 8% (4 ticks of 2% per second) of his max HP and mana per second while.

Mana Affecting Abilities

 * Ana's level 10 heroic Nano Boost restores 200 mana to an allied Hero.
 * Arthas' trait Frostmourne Hungers restores mana on-hit.
 * His level 1 talent Eternal Hunger increases the mana restores by 4 on hitting a hero, up to 40.
 * Gul'dan's trait Life Tap prevents him from naturally regenerating mana, but can be activated to drain health to restore mana with no cooldown.
 * His level 4 talent Improved Life Tap increases the mana restored.
 * Leoric's ability, Skeletal Swing, refunds 50% of its mana cost if it hits an enemy hero.
 * Malfurion's trait Innervate restores Mana to a target ally while reducing their cooldown as well.
 * His level 13 talent Revitalize causes it to affect himself restoring 50 mana.
 * Nazeebo's Trait Voodoo Ritual causes enemy minions killed while afflicted with his trait to grant a permanent 1 mana.
 * His level 4 talent Blood Ritual causes enemies killed while afflicted with his trait to restore 2% of his max mana.
 * His level 4 talent Hexed Crawlers causes Corpse Spiders to restore 1% of his max mana whenever they attack.
 * His level 4 talent Big Voodoo increases the mana gained by his Trait by 100%.
 * Probius' trait Warp In Pylon prevents him from naturally regenerating mana, but restores mana rapidly while he's inside a Pylon's Power Field.
 * Tassadar's trait Resonance Beam grants him increased mana regeneration based on how much Resonance he has, up to 100%. At maximum Resonance, he also regenerates a flat amount of mana per second.

Mana Affecting Talents

 * Blaze's level 1 talent Neural Stimpack restores 50 mana while reducing ability cooldowns as well.
 * Diablo's level 1 talent Devil's Due increases the mana regen of globes and Healing Fountains by 2% per soul.
 * Falstad's level 1 talent Gathering Storm restores 10 mana for each Hero hit by Hammerang.
 * Greymane's level 4 talent Insatiable causes Inner Beast to restore 10 mana for each basic attack.
 * Jaina's level 1 quest talent Fingers of Frost grants .1 mana regen for each globe collected up to 2 per second.
 * Jaina's level 4 talent Arcane Intellect causes damage dealt to chilled targets to restore mana, 5 for basic attacks, 20 for abilities.
 * Kael'thas' level 1 quest talent Mana Addict grants 15 max mana for each globe collected.
 * Kael'thas' level 4 talent Mana Tap restores 4% of his max mana upon using Verdant Spheres.
 * Kharazim's level 1 trait Insight restores mana every 3rd basic attack.
 * Kharazim's level 20 active talent Epiphany restores 33% of his max mana.
 * Leoric's level 1 talent Fealty Unto Death causes minions that die nearby to restore 5 mana.
 * Li-Ming's level 1 talent Astral Presence increases mana regen by 100% when below 25% mana.
 * Li-Ming's level 1 talent Power Hungry increases mana gained by globes by 100%.
 * Li Li's level 1 talent Eager Adventurer increases her mana regen by 150% while Fast Feet is active.
 * Medivh's level 1 talent Raven's Intellect Raven Form increases Medivh's Mana and Health Regeneration by 75%
 * Medivh's level 20 talent Arcane Brilliance active talent restore 200 mana to all nearby allied Heroes
 * Nova's level 1 talent Advanced Cloaking increases mana regen by 2 while cloaked.
 * Rehgar's level 4 talent Feral Heart causes basic attacks in Ghost Wolf form to restore 1% of his mana, increased to 5% against heroes.
 * Tassadar's level 1 talent Psi-Infusion restores 0.5 mana each time Psionic Storm damages a non-structure, doubled against heroes.
 * Thrall's level 1 talent Rolling Thunder causes his first basic attack against enemy that was recently hit by Chain Lightning restore 12 mana.
 * Thrall's level 4 talent Mana Tide restores 15 mana when Frostwolf Resilience triggers.
 * Uther's level 1 talent Wave of Light restores 5 mana for every allied or enemy hero affected by Holy Radiance.
 * Uther's level 1 quest talent Hammer of the Lightbringer restores 1.5% of his max mana with each basic attack.
 * Xul's level 7 talent Trag'Oul's Essence restores .5% of his max mana whenever a Skeleton attacks.