The I-field generator is a fictional piece of technology from the Gundam Universal Century that consists of a special shield generator that provides a 360-degree barrier of protection against beam weapons. I-field generators were designed mainly for use in mobile armors, which for the most part were unable to carry laminated armor shields like most mobile suits of the time. Initially, I-field generators were too bulky to be mounted on mobile suits, but by the end of the first Universal Century mobile suit-sized I-field generators were feasible, if not cost-effective.

This technology was first utilized in the One Year War, and installed on the massive Principality of Zeon mobile armor MA-08 Big Zam , piloted by Dozle Zabi. The two I-field generators protected the Big Zam from beam weapons. However, the I-field had a major weakness - it provided no protection against traditional kinetic or hand-to-hand weapons. Dozle discovered this flaw the hard way, when Amuro Ray, piloting his RX-78-2 Gundam mobile suit engaged the Big Zam with his Gundam's beam saber and broke through the I-field barrier, allowing Amuro to destroy the Big Zam. The I-field technology would later be utilized in other mobile armors, most notably the Delaz Fleet mobile armor AMA-X2 Neue Ziel, now remamed AMX-002; and the Earth Federation's RX-78GP03 Gundam Dendrobium mobile armor, in the last battle of the Delaz Conflict. This technology would later also be utilized in the powerful RX-93 Nu Gundam, again piloted by Amuro Ray, and used in the Nu Gundam's psychoframe controlled "fin funnels".

A relative of the I-field generator appeared in the After Colony timeline. Called "planetary defensors", these small disklike drones would be separated from the mobile suit, and arrange themselves to deploy a shield that would protect the mobile suit. The OZ-13MSX2 Mercurius mobile suit was developed as a testbed for the planetary defensor system by OZ, which later integrated the defensors into the OZ-02MD Virgo mobile doll. A Virgo on its own can only generate a shield that protects from fire in one direction (as one Virgo only carries four defensors) - however, three Virgos working in concert can deploy their defensors in a globular shield, as can the Mercurius (which carries ten defensors.) The splinter group White Fang deployed an advanced variant of the Virgo, the WF-02MD Virgo II , which carried eight defensors per unit.

The inverse of the I-field generator concept is the Cosmic Era's Phase Shift armor, which counters physical attack but is vulnerable to beam weaponry.