Energy shielding

Summary
Shields, which are generated by MJOLNIR armor or the Elite's armor, provide the user with an extra layer of armor but its strength differs hugely from difficulty to difficulty. It will protect their Health from damage until it is depleted, and it will regenerate after a while, provided that the user is not injured during this time. In Multiplayer, you can have 50%, 100%, 200%, 300% or 400% shield, or none at all. In Halo 1 it is shown at the top-right corner of the screen, in Halo 2 it is in the bottom-left, and in Halo 3 the top-center. They have been changed since Halo: CE by making it charge faster and more resistant.

Be forewarned, although the shield protects your health, it doesn't render you invincible. Pay attention to your shield meter, and if it is depleted, seek cover until it regenerates. Also, it will not protect you from everything, and rockets, grenades, sniper bullets, and some other weapons may shred right through it.

Another type of shield is the one found on Covenant Starships, and is a light-gray color. The shields can take a vast amount of punishment, and can recharge very quickly. It can absorb anything less then a direct nuclear missile, and a MAC round. The only downfall is when the vessel fires its plasma weapons, The ship needs to drop a section of its shields for a fraction of a second.

Human Shielding
Halo: Combat Evolved

Unlike the Covenant Elite's Personal Energy Shield, the MJOLNIR uses a reversed engineered Jackal Arm Shield that has been modified into a full body shield, much like a Covenant Elite's. The major differences in it that once the human shield takes damage it glows gold. The Covenant ones glow blue. The color difference is speculated to be because of the two technologies being different. It also seems that the shielding used by the humans has different defensive properties to the Covenant Elite's, appearing more supceptible to plasma-based weaponry (e.g. the Covenant Plasma Pistol, especially overcharged) than to ballistic weaponry (e.g. the UNSC Assault Rifle).

Halo 2:

In Halo 2, your shields can be stripped in seconds if you're not careful. On Legendary, a single melee strike from an Elite can end your life, whereas it takes five melee strikes with the SMG to take down an Elite's shield. Also some high-ranking Elites' shields can withstand a plasma grenade detonation, even when stuck.

Halo 3:

Not much is known about Halo 3 shielding save for that it will return. It is assumed that it is the best to date that humans can produce. It is also know that the Shield Grenade is ONI tech.

Covenant Shielding
Halo: Combat Evolved

Unlike the humans, the Covenant have a very extensive knowledge of shielding equipment and it's uses. Examples of this excellent understanding are every where. Elites, Jackals, Floor Mounted Shields, and Ship Shields are just some of the basic examples. The greatest example of the Covenant's understanding is that of body shielding, as all Elites, except for Stealth Elites, use it. If the Covenant hardly understood it, they would not have it main stream.

Halo 2:

Not only have the Covenant shields advanced, their ease of use has too. Even the lowliest Elite can use the shields with great ease. Also, the Covenant have discovered how to run Active Camo and Shielding at the same time. Not only that, but Tartarus, the Chieftain of the Brutes, was equipped with a personal shield. The frightening possibility that more Brutes are equipped with this has become apparent.

Halo 3:

Just like the humans, shielding is expected to return. Also, because the Brutes have taken over, more Brute controlled personal energy shields are likely to appear.

Starship Shielding
The only known starships to have shields are Covenant ships. All Covenant vessels are protected by a highly resistant energy shield that can recharge over time. Most Human weapons cannot penetrate the shields, only MAC rounds and Shiva nukes can get though. The only downfall is when the vessel fires its plasma weapons, the ship needs to drop a section of its shields for a fraction of a second.

Related Links

 * Elite Personal Energy Shield
 * Jackal Personal Arm Shield