Energy shield

Energy shield acts as an additional hit point pool on top of life. If you have any energy shield remaining when you take damage, the damage is subtracted from the energy shield first. Damage is only applied to life once all energy shield is depleted. The exception to this is chaos damage, which ignores energy shield.

Energy shield will recharge if you do not take any damage for a certain period of time. By default, the delay period is 6 seconds. This time can be reduced with Increased Energy Shield Cooldown Recovery modifiers from passive skills and equipment. The formula is delay = 600 / (100 + increased recovery%), so having a 100% modifier gives a delay of 3 seconds.

As long as you have greater than 0 energy shield, you have an implicit 50% chance to avoid being stunned.

The aura Discipline increases the energy shield of you and nearby allies.

Passives

There are passive skill nodes that grant additional energy shield or a combination of bonuses including energy shield. Other passives such as Energy Shield Delay decrease the cooldown delay for energy shield to be restored after taking damage.

Energy Shield

These passives increase maximum energy shield by a percentage.

Energy Shield on Shield

These passives increase the energy shield bonuses of equipped shields by a percentage.

Energy Shield Delay

These passives decrease the cooldown delay for energy shield to be restored after taking damage.

Miscellany

These passives are related to energy shield, but don't fit into any other category.