Cooldown reduction

Cooldown reduction reduces the cooldown of abilities, or the amount of time you must wait after casting an ability before that ability can be utilized again. Cooldowns cannot be reduced by more than 40%.

Cooldown reduction works additively. If you have a 6% cooldown reduction from masteries, and a 10% cooldown reduction from you will have a 16% cooldown reduction.

Items that reduce cooldown
There are several items which reduce the cooldown of your abilities. Cooldown Reduction granted by an item is always Unique Passive.
 * +10% Cooldown Reduction. +30 AP, +7 Mana Regeneration per 5. 1245 Gold.
 * +20% Cooldown Reduction. +425 Mana, +45 Armor. 1675 Gold.
 * +15% Cooldown Reduction (at 20 stacks). +20 AP, UNIQUE Passive: Your champion gains 8 ability power per stack, receiving 2 stacks for a kill or 1 stack for an assist. This effect can stack 20 times; you lose a third of your stacks if you die. 1235 Gold.
 * +15% Cooldown Reduction (to allied nearby champs). +520 Health, UNIQUE Aura: Gives nearby Champions 12 Mana per 5. 2285 Gold.
 * +12% Cooldown Reduction. +33 Magic Resistance, +20 Health Regen per 5, UNIQUE Passive: Increases healing and regeneration by 25%. 1250 Gold.
 * +10% Cooldown Reduction. +40% Attack Speed. 1140 Gold.
 * +10% Cooldown Reduction. +25 Attack Damage, UNIQUE Passive: +15 Armor Penetration. 1337 Gold.
 * +15% Cooldown Reduction. +60 AP, +10 Mana Regen per 5, UNIQUE Active: Deals magic damage to target champion equal to 30% of their current health (+3.5% per 100 Ability Power) with a minimum of 200 damage. 1 minute cooldown. 2610 Gold.
 * +25% Cooldown Reduction. +50% Attack Speed, +55 AP, +10 Mana Regeneration per 5. 2885 Gold.
 * +15% Cooldown Reduction. +30 Attack Damage, +15% Critical Chance, UNIQUE Passive: +20 Armor Penetration, Unique Active: You gain +20% movespeed and +50% attack speed for 4 seconds. Attacking enemy units with melee attacks increases the duration by 2 to a maximum of 8 seconds. 60 second cooldown. 2687 Gold.
 * +15% Cooldown Reduction. +300 Health, +90 Armor, +25 Health Regen per 5 sec, UNIQUE Passive: 20% chance on being hit to slow the attacker's movement and attack speeds by 25% for 3 seconds, UNIQUE Active: Slows movement speeds and attack speeds of surrounding units by 35% for 1 second + 0.5 seconds for each 100 Armor and Magic Resist. 60 second cooldown. 2925 Gold.
 * +25 Cooldown Reduction. +99 Armor, +500 mana, UNIQUE Passive: Reduces the attack speed of nearby enemies by 20%. 2800 Gold.

Other Ways to reduce Cooldowns

 * Sorcery (Offense Mastery): +0.75% Cooldown Reduction per Rank (max. +3% at Rank 4).
 * Intelligence (Utility Mastery): +2% Cooldown Reduction per Rank (max. +6% at Rank 3).
 * Celerity Runes (see Rune List)
 * Focus Runes (see Rune List)
 * Some Champions have abilities which can decrease their cooldowns (ie. Heimerdinger's UPGRADE!!!)

Updates
Due to recent updates this article might not be actual. It was last updated during Patch 1.0.0.86. If there is a new version out, please check the data frequently.