Might and Magic Edit
Heroes of Might and Magic Edit
Spell points have been part of the Heroes series since Heroes II, where it replaced the spell memorisation system used in Heroes I. Every spell that the hero learns, remains in their spellbook, but they can only cast it if they have sufficient spell points, and higher-level spells cost more spell points.
Spell points are usually tied to the knowledge skill: every point in knowledge gives 10 spell points. Some skills can increase a hero's spell points, like the intelligence skill in Heroes III and Heroes V. Items that increase their knowledge, like the Foremost Scroll, naturally also increase their spell points.
In Heroes IV, spell points are instead tied to the subskills of the magic schools: every magic school has a subskill that increases spell points, and spell point regeneration. For example, the Order Magic subskill is Enchantment. There are also some artifacts that increase spell points, like the Supreme Crown of the Magi.