Life
Life is shown as a red orb in the lower left of the screen and will decrease as you receive damage. Characters die when they reach 0 life and must be resurrected in town. You can restore life by using flasks, gaining life regeneration from passive skills and equipment, or leeching life from enemies. Life is fully restored when you enter a town.
Every class starts out with 50 Life, and gains +12 per level giving a base life of 1238 at level 100. Strength increases Life, with every +10 node giving +5 Life. Characters do not begin with any life regeneration, but it is available from gear and passive skills.
New Formula for Forsaken Masters:
Maximum Life = (38 + (Level * 12) + (Strength / 2) + additive modifiers) * (100% + multiplicative modifiers)
Old Formula:
Maximum Life = (42 + (Level * 8) + (Strength / 2) + additive modifiers) * (100% + multiplicative modifiers)
Additive modifiers are added directly to your base life (+x to maximum life). Multiplicative modifiers apply to additive modifiers as well as base life and strength (+x% increased maximum life). See Modifiers.
Passives
There are passive skill nodes that grant additional life or a combination of bonuses including life. Other passives such as Life Regeneration and Life Leech are related to life, but do not increase maximum life.
The Chaos Inoculation Keystone will reduce your Life to one, nullifying any low-life spell damage bonuses, as well as any increased life or life regen passives taken. Pain Attunement will increase your spell damage if your Life is at or below 35% (this can be achieved through Blood Magic and reserves). Blood Magic removes your Mana, letting you use your Life to cast spells.
Please see the Minions page for information on Minion Life and the passives associated with them. Passives also exist which will increase the amount of Life regained from Flasks, as seen here.
Life
These passives either add a set amount to a character's maximum life or increase maximum life by a percentage.
Life Regeneration
By default characters do not regenerate life, but it is available from gear and passive skills. The following passives increase life regeneration as a percentage of maximum life per second.
Life Gain on Hit
When an enemy is hit by your attack, you gain an amount of life equal to combined life gain on hit bonuses from passives and all other sources. This applies to each enemy hit by your attacks, so a single attack that hits multiple targets can trigger more than one life gain on hit effect. Unlike life leech, life gained this way is restored instantly.
These passives add a set amount of life gain on hit to attacks.
Life Gain on Killing Blow
When an enemy is killed by your attack, you gain an amount of life equal to combined life gain on killing blow bonuses from passives and all other sources. This effect triggers once for each enemy killed. Unlike life leech, life gained this way is restored instantly.
These passives add a set amount of life gain on killing blow to attacks.
Miscellany
These passives are related to life, but don't fit into any other category.