A powered exoskeleton is a mobile armored defense system consisting primarily of a skeleton-like framework worn by a person and a power supply that supplies at least part of the activation-energy for limb movement.
Powered exoskeletons are designed to physically assist and, in many cases, protect the wearer. They may be designed to assist and protect soldiers and construction workers, or to allow people to survive in other dangerous environments. A wide medical market exists for powered exoskeletons to provide mobility assistance for aged and infirm people. Other possibilities include rescue work, such as in collapsed buildings, in which the device might allow a rescue worker to lift heavy debris, while simultaneously protecting him from falling rubble.
While it is the most successful UNSC powered armor project, MJOLNIR is by no means the only effort to physically augment soldiers in combat. The HRUNTING Mark III (B) Exoskeleton and the HRUNTING/YGGDRASIL Mark I were exoskeleton systems derived from the earlier prototypes from the exoskeleton program which predated MJOLNIR. Large-scale powered exoskeletons became more common in the years following the Human-Covenant War, with at least one model, the Mantis, seeing battlefield use.
RKD, an Earth think-tank, created the HAYABUSA project concurrently with MJOLNIR and while the two were developed separately, they share many characteristics, and are interchangeable to a degree. SPARTAN-III supersoldiers used Semi-Powered Infiltration armor which, despite lacking the strength- and speed-augmentation capabilities of MJOLNIR, provides effective active camouflage by means of photoreactive panels, allowing covert operations in enemy territory. The Forerunners developed combat armor suits known as combat skins, using a class system based on numbers, on which the MJOLNIR Mark V and Mark VI would be rated Class 2.
 Known powered exoskeletons
- Cyclops Mark II
- Hayabusa Powered Assault Armor - A UNSC powered armor system similar to the MJOLNIR armor.
- HRUNTING Mark III (B) Exoskeleton
- HRUNTING/YGGDRASIL Mark I Prototype Armor Defense System - An advanced development of the early MJOLNIR system.
- HRUNTING/YGGDRASIL Mark IX Armor Defense System - A powered exoskeleton/armored fighting vehicle used by the UNSC Marine Corps after the Human-Covenant War.
- MJOLNIR Powered Assault Armor - The performance-enhancing body armor used by the SPARTAN-IIs.
- Semi-Powered Infiltration armor - The armor used by the SPARTAN-IIIs.
- ^ Halo: The Essential Visual Guide, page 44
- ^ Halo 3
- ^ Halo: Ghosts of Onyx, page 16
- ^ Halo: Combat Evolved, campaign level The Library
- ^ Halo 3, campaign level Halo