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.

Dexterity modifiers are applied to:

• Ranged attack rolls, including those for attacks made with bows, crossbows, throwing axes, and other ranged weapons. (unless creature has Zen Archery and higher Wisdom)
• Melee attack rolls with Weapon Finesse
• Dodge Armor class (AC), provided that the character can react to the attack.
• Reflex saving throws, for avoiding fireballs and other attacks that you can escape by moving quickly.
• Hide, move silently, open lock, parry, sleight of hand, and tumble checks. These are the skills that have Dexterity as their key ability.
• Initiative rolls
• When applying bonus damage per round from Expose Weakness