Welcome to my Irelia Dominion Guide.
Irelia is very strong and very uselful in League of Legends: Dominion, she is a great Tank and deals tons of damage even when built as Tank.
Irelia's key item is Trinity Force, it gives her great mobility and even greater damage and some survivability, too.
I think Irelia shines best as a Taker or a Defender.
Her strengths are at 1v1 and she can farm minions pretty easily, too.
I think Irelia can be played as a Capturer, too, but I think as a Taker/Defender, she is much more useful, because in most cases you have got a Rammus/Evelynn in your team, who are better at this.

Pros:
Defender Irelia:
-High survivability
-High damage
-can Tank very much
-Can even fights 1v2, 1v3(only squishies)
-Easy Tower Diving
-OP IN DOMINION!!!

Taker Irelia:
-High damage output
-High mobility
-Shines at 1v1
-Strong in Team Fights
-Can even take tanks down
-OP IN DOMINION!!!

Cons:
Defender Irelia:
-Average against another Irelia(if good)
-Can be dominated if ganked too much
-Think about more

Taker Irelia:
-Average survivability
-Easy to focus
-more a 1v1 champion(in some cases 1v2)
-Easy to be Assassined

Obviously, the Runes for Defender Irelia are:
Magic Pen.
Flat Armor
Magic Resist per Level
Flat HP
this Runes setup gives you great Defense and you can stay on your "lane" for a long time, farming.

The Runes for Taker Irelia are more versatile and can be like that:
Armor Pen. or Attack Speed
Armor per Level
Magic Resist per Level
Armor Pen. or Flat HP or Movement Speed
This gives you great damage and a bit survivability, so you can kill enemies more efficiently

First of, Defender Irelia takes full Tank Masteries; 1/22/7
you take any Defensive Mastery you can take and Mobility is also useful due to your lack of escape mechanism.
Upgrading your ghost and reducing its cooldown is also very useful.
As Taker Irelia you focus on high-damage Masteries and play 21/9/0 for some extra durability.
These Masteries are very strong and give Taker Irelia at least some "durability" and Defender Irelia some utility.

Defender Irelia is very versatile at starting Items, you can take Phage, Sheen or even Giant's Belt with Defender Irelia, I take Phage because this slow can give you early kills, when it pros. Your first big Item is always Trinity Force and then Wit's End for some Magic Resist and AS.
After Boots you buy a Force of Nature, in some cases you can play Thornmail, when the enemy team hasn't got much Magical Damage. Instead of these Items i take Hextech Sweeper, to counter Twitches, Evelynns or Shacos. Your Last 2 Items are always Warmog's Armor and Atma's Impaler, in some cases you buy Atma's Impaler first and the Warmog's Armor.

Taker Irelia focuses on high-damage Items, like Kitae's Bloodrazor and Infinity Edge.
Your starting Items are Prospector's Blade and Boots of Speed, you should take Potions, too, they are very useful because you don't build Tank.
After Trinity Force start building Infinity Edge and Kitaes Bloodrazor, to shred enemy Tanks and Squishies much faster.
I play Sanguine Blade very often because of its high Damage and Life steal.
In some cases it is useful to buy survivability Items instead of the Sanguine Blade, but in some cases, when you are not the enemies' focus, you buy Sanguine Blade.
To round up your built, buy Odin's Veil for much Durability and some Ture Damage.

As Defender Irelia max W first and then E for True damage and nice sustainability, E for very high damage. It is obvious that you skill your ult, whenever you can. Max Q last, it is just a charge and you don't want to loose the stun length of your E.

As Taker Irelia you max Q first for damage and then E, this maximizes your damage output. Again, skill your Ult whenever possible. Max W last, you don't need it if you focus the right targets, believe me.

As Defender Irelia you play with the Summoner Spells Promote and Garrison.
Promote gives you great pushing ability and with Garrison you can tower dive in early levels.
You can take Ghost instead of Garrison, but I really like to tower dive the enemies.

As Taker Irelia you take Summoner Spells to catch enemies and finish them if your skills are on CD. You can take exhaust instead of Ignite, to get away from a bunch of enemies.

Defender Irelia is focused on 1v1 the bottom lane, but in Team Fights she can jump from target to target and focus the right enemies!

Taker Irelia can be killed VERY fast in Team Fights, if focused, if not she can kill 1 after the other.

Irelia's Anti-Tank Skill is useful if the other ones are gone, low or even dead.
SHE CAN FOCUS TANKS!!!!!!!

Always farm if you play Defender Irelia, pus with Ulti and Promote, it works!
If you play Taker Irelia you should focus on Champion Kills and not on minions. but always farm if you are left alone by the enemy Team.

All in all Irelia is in my opinion the most OP Champion in League of Legends: Dominion, Her Taking is very strong, and her Defendability is even better.

26.10.2011 18:24 Added some Items which can, and should be used instead.
14.12.2012 20:13 Changed Runes and Masteries to S3. Changed some Items for both Taker and Defender Irelia.