Dexterity measures hand-eye coordination, agility, reflexes, and balance. This ability is the most important one for rogues, but it’s also high on the list for characters who typically wear light or medium armor (rangers and barbarians) or no armor at all (monks, wizards, and sorcerers), and for anyone who wants to be a skilled archer.
You apply your character’s Dexterity modifier to:
o Ranged attack rolls, including those for attacks made with bows, crossbows, throwing axes, and other ranged weapons.
o Armor Class (AC), provided that the character can react to the attack.
o Reflex saving throws, for avoiding fireballs and other attacks that you can escape by moving quickly.