Monsters of the regenerative enemy type recover a certain amount of HP per turn; this was intended to be 2 HP in the NES version, but due to a bug this never occurs. In all other versions, this trait works, and restores HP equal to 5% of the monster's maximum HP.
Playable characters are able to access a slightly more potent version of this effect with the Lordly Robes, which restores 10% of their maximum HP per turn. Only White Wizards are able to equip the Lordly Robes, and thus (barring using the equipment glitch) they are the only characters able to get any regeneration effects.
Auto Regen is granted to any character equipped with the Protect Ring.
The Angel Ring grants Auto-Regen to the wearer. A side effect of having Auto-Regen is that the wearer becomes immune to Sap. Enemies that has the Regen status innately cannot be removed by Dispel, and as such, it is permanent. Gau and Gogo under the Rage status can gain this ability permanently when using specific Rages.
Auto-Regen is a support ability learned by all characters. It is learned from the Golem's Flute, Golden Hairpin, Carabini Mail, Brave Suit, Light Robe, Glutton's Robe, Angel Earrings, and Maiden Prayer and takes ten Magic Stones to equip.
The AP costs are as follows: 25 AP for Zidane and Freya, 30 AP for Vivi and Quina, 35 AP for Dagger, Eiko and Amarant and 75 AP for Steiner. Auto-Regen is especially useful, because it heals even during attack animations, such as eidolon summon animations.
Auto Regen is a job trait that restores 1 HP per tick. It is learned by White Mage (level 25), Carbuncle (level 25), Light Spirit 25), and Blue Mage (level 16). Blue Mages can obtain this job trait by setting both Sheep Song and Healing Breeze.
Auto Regen II is a job trait that restores 2 HP per tick. It is learned by White Mage (level 76).
Auto Regen is also granted by certain gear. Auto Regen gained from gear stacks on top of itself and on top of the job trait, granting more HP restoration per tick.
In the Zodiac versions, the Ribbon now also grants constant Regen and Libra in additional to providing immunity to all negative statuses.