Mana regeneration

Mana Regeneration (also known as Mp5 or mana per 5 seconds) is a statistic that determines the amount of mana that a champion regenerates over a five second period. Each champion starts with a certain rate of base mana regeneration. This statistic scales additively; meaning that each bonus point acquired directly affects the statistic. The player can also use (a summoner spell) to restore mana.

Items

 * +25 MP5, +400 Mana, +45 AP, Passive: 3% of your Max Mana is converted to Ability Power. UNIQUE Passive: Each time your Champion uses an Ability their Maximum Mana will increase by 4 Mana. This effect has a 3 second cooldown..
 * +7.5 MP5, +30 Magic Resistance, Unique Passive: Increases your Mana Regen by 1% per 1% Mana you are missing..
 * +10 MP5, +60 AP, UNIQUE Passive: Reduces ability cooldowns by 15%. 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..
 * +5 MP5, +15 AP, +100 Health..
 * +20 MP5, +25 Hp 5, +25 Tenacity..
 * +3 MP5..
 * +7 MP5, +30 AP, UNIQUE Passive: Reduces ability cooldowns by 10%..
 * UNIQUE Aura: 7.2 MP5 to nearby friendly Champions..
 * +7MP5, +350 Mana, +20 Attack Damage, UNIQUE: 2% of your max Mana is converted to Attack Damage, UNIQUE: Each time you attack, you gain one maximum mana (3 second cooldown). Each time you use an ability, you gain four maximum mana (3 second cooldown). Bonus caps at 1000..
 * +7 MP5..
 * +12 MP5, +75 AP, UNIQUE Passive: Reduces ability cooldowns by 20%..
 * +10 MP5, +50% Attack Speed, +55 AP, UNIQUE Passive: Reduces ability cooldowns by 25%..
 * +8 MP5, +18 Health Regen per 5 sec, UNIQUE Passive: Gain an additional 5 Gold every 10 seconds..
 * 7 MP5, +30 Ability Power. Unique Passive: +200 Health..
 * +520 Health, UNIQUE Aura: Gives nearby allied champions +12 MP5 and 10% reduced Cooldowns..
 * +15 MP5, +330 Health, +30 Health Regen per 5 sec, UNIQUE Passive: Reduces ability cooldowns by 15%, UNIQUE Active: Nearby champions gain 40% movement speed for 3 seconds (60 second cooldown)..
 * +7 MP5, +350 Mana, UNIQUE Passive: Each time your Champion uses an Ability their Maximum Mana will increase by 4 Mana, up to a maximum of twice in a six second period; bonuses cap at +1000 Mana..
 * +5 MP5, +50 Attack Damage, +15 Health Regen per 5 sec, Passive: Your attacks Splash, dealing Physical Damage in a small area around the target.

Champion Abilities

 * increases his mana regeneration by 35 / 50 / 65 for 25 seconds.
 * increases his mana regeneration by 0.75% per 1% mana he is missing.

Masteries

 * increases your champion's mana regen per 5 sec. by 1/2/3.
 * increases your champion's total mana regeneration by 2/3/4%.

Runes

 * and runes increase mana regeneration.

Neutral Buffs

 * The buff regenerates 1.5% of your max mana per second for 2.5 minutes.
 * The buff gives 1% of your max mana in mana regen per 5 sec. for 4 minutes.

History
As of the patch V1.0.0.110, all champions with mana had their base mana regen increased by 2.5 and mana regen per level increased by 0.2. Mana regen runes and masteries were also reduced by about 33%.