Constitution represents your character’s health and stamina. A Constitution bonus increases a character’s hit points, so the ability is important for all classes. Some creatures, such as undead or constructs do not have a Constitution score.
You apply your character’s Constitution modifier to:
- Each roll of a Hit Die (though a penalty can never drop a result below 1 — that is, a character always gains at least 1 hit point each time he or she advances in level).
- Fortitude saving throws, for resisting poison and similar threats.
- Concentration checks. Concentration is a skill, important to spellcasters, that has Constitution as its key ability.
If a character’s Constitution score changes enough to alter his or her Constitution modifier, the character’s hit points also increase or decrease accordingly.