Shields are an excellent way to improve your defense. Shields increase your Defense Rating and provide heroes with a Chance To Block incoming attacks (effectively reducing damage of those attacks by a fixed amount). Some classes like Paladins and Crusaders rely more heavily on shields than others, though with the introduction of Hardcore, there are respectable builds for all classes that involve a shield.
"The hero who wields a shield in their off-hand is giving up the capacity to hold killing devices in both hands or carry a power-enhancing item, but choosing to do so can save their life, or at least prolong it a few seconds under a storm of arrows or claws."— Game Guide(src)
All shields occupy the off-hand slot, so equipping a Two-handed weapon with a shield is impossible unless one of two conditions is fulfilled:
- The user is a Crusader with the passive skill Heavenly Strength. This will give them the choice of any Two-Handed melee weapon, as long as a Shield is equipped.
- The user is a Barbarian attempting to use a two-handed weapon. Due to their great strength, the Barbarian can choose to wield a two-handed sword with one hand, while being able to equip a shield, or another feasible weapon in his offhand.
- This point is more easily seen in the Hellfire expansion to the original Diablo, while nonexistant in Diablo III. In Hellfire, the Barbarian could choose to use a Two-handed Sword or Mace in one hand, with a Shield in the other hand. This was limited to two-handed swords in the second game and penalized the damage dealt on successful hits, but in return the Barbarian gained the ability to dual wield these weapons. Their capabilities to use a two-handed weapon in one hand have been straight up removed in the third game, replaced by Mighty Weapons.
Shields in Diablo I and Hellfire function at their most basic levels. Provided you have a Shield but no melee weapon equipped, you can use a shield to minimally damage your enemies. They are best in the hands of a Warrior or a Barbarian wishing to use blunt weaponry, because not only do they possess the natural Strength needed to equip the higher end shields, but they naturally possess Fast Block as well which means that they do not need any shield giving faster blocking like Stormshield, therefore they're better off with Magical Shields in their hands giving even greater Armor Class than the formerly mentioned one, combined with bonus Health. A hero's Chance To Block is not limited by a hard cap, so one could bring their Dexterity high enough to guarantee blocks against melee and ranged attacks.
Diablo II/Lord of Destruction
Shields in Diablo II/Lord of Destruction have some new tricks unto them, compared to Diablo I/Hellfire. To name one, there are certain Totems only usable by the Necromancer, and there are certain Paladin Shields which only the Paladin can equip. Another example is the Paladin's Smite Skill, which allows him to stun and knock back his foes by bashing them with his shield (and cannot be used if no shield is equipped). Chance To Block has a hard cap of 75% when immobile, walking or attacking, and 25% when running. Having an increase in Dexterity will contribute to a higher block chance, as well as the Paladin's Holy Shield Skill.
Shields return in Diablo III/Reaper of Souls, but their functions are nerfed down from that of Diablo II / Lord of Destruction. A successful Chance to Block is a bit more difficult to attain, due to the fact that Shields cannot roll higher than 20% Chance to Block without affixes that increase said chance (up to 31% total). They also do not block all damage when they do block an attack. Instead, each shield carries a Block Amount, seen under its Chance to Block. They do, however, contribute the most Armor out of any equipment type, being the only piece able to achieve 1,000 Armor (on level 60) and 2000 Armor (on level 70) without Ancient Legendary bonus or affixes that increase Armor or Strength.
Shields may also roll reduced damage from elites, bonus damage to elites, reduced damage from melee / ranged attacks, Critical Hit chance, reduced resource costs, increased Life and Life regeneration, increased healing, Thorns, status effect duration reduction, all resistances, a socket, and various 'on hit' effects.
Like Paladins in Diablo II, Crusaders have their own type of shields: Crusader Shields. Some of Crusader skills can only be used with a Shield equipped in the off-hand.
In addition, force fields protecting the character from harm ('bubbles' granted by certain abilities) are also generally called Shields.