Orianna is somehow different from any other hero in the league. Not only her appearance, but also the playstyle is quite different from most characters. I think she is rather hard to play, so if you are new, you should probably start with an easier hero.

v1.00 2nd June 2011
First build published.

v1.01 3rd June 2011
Changed build to have more mana regeneration.

v1.02 4th June 2011
Added item explanations for items fitting good to Orianna.

v1.03 5th June 2011
Tips and Tricks section added.

Magic penetration marks ( Greater Mark of Magic Penetration) do a great job in terms of damage. Furthermore Orianna needs lots of mana, so I use some mana regeneration done by seals ( Greater Seal of Replenishment). Magic resistance is also quite helpful, so that you can't be taken out so easily by spells early on ( Greater Glyph of Magic Resist). For quintessences you have more than one good way to do it, I think movement speed is never wrong ( Greater Quintessence of Movement Speed), but you can also go for cooldown reduction ( Greater Quintessence of Cooldown Reduction) or AP ( Greater Quintessence of Ability Power, Greater Quintessence of Scaling Ability Power).

Mana regeneration and cooldown reduction is important for Orianna, so I think this mastery build is quite advantageous. I have also spent some points on defense, so that she cannot be taken out so easily at the beginning.

I think there is no optimal build, it always depends on your opponents, your playstyle and the whole situation you are in. This item builds should only give you a basic direction, whereof you should probably differ from depending on the factors mentioned above.

Start Items

Doran's Ring

This item gives you a good boost to your HP and also some ability power and mana regeneration, which is good for playing Orianna early on.

Regrowth Pendant

When you think you are on a lane where you get harassed by auto-attacks easily and might not get so many creep kills you can buy this item at start and go for Philosopher's Stone, which gives you good health and mana regeneration for early game and 5 Gold every 10 seconds.

Ruby Crystal

If you do not want to spend money on items, you have to sell later on, you should get Ruby Crystal. This item gives you lots of HP, which is really perfect for Orianna in early game and can be built to Catalyst the Protector and Rod of Ages later on.

Boots

Sorcerer's Shoes

Magic penetration means dealing more damage with your spells, so this shoes do a great job on Orianna.

Ionian Boots of Lucidity

If you prefer to use your skills more often, buy this boots, which give you a little cooldown reduction.

Mercury's Treads

Buy this boots if the opponent team has a lot of stuns, slows and taunts. This item gives you better survivability in that case and additionally also a little magic resistance.

Boots of Swiftness

This boots are hardly needed, but in some cases, where the opponents have high movement speed you might want to buy this kind of boots.

Core Items

Archangel's Staff

This item gives you plenty of mana and mana regeneration, so that you can spam your spells even for creep kills. Furthermore you also get more ability power to power up your skills.

Rod of Ages

This item should be bought very early, so that you can use its full capacity, because it gets better over time. It gives you lots of HP, ability power and mana, what really fits well to Orianna's needs.

Rabadon's Deathcap

This item gives you a great boost to your ability power, so it improves your skills. Therefore it is quite powerful.

Situational Items

Lich Bane

This is also a good item which increases your ability power, movement speed, mana and gives you a little magic resistance. Therefore a great choice for Orianna.

Rylai's Crystal Scepter

This item really helps you in terms of survivability, because it adds HP and slows enemies also with your Command: Attack and Command: Protect spells. Furthermore it is easier to do spell damage when the opponents are moving slower and it adds ability power to power up your skills. So it is quite useful for a lot of situations.

Zhonya's Hourglass

This item adds ability power, armor and the passive can be useful, when you are focused in team fights so they cannot attack you for some seconds while your team mates kill them and/or to wait for your skills to be available again.

Void Staff

Buy this item, when your opponents stack magic resistance to have at least 40 percent magic penetration.

Abyssal Scepter

Abyssal Mask gives you ability power, magic resistance and a little magic resistance reduction.

Morello's Evil Tome

This item adds ability power and mana regeneration, if you feel your mana still gets low too easily.

Deathfire Grasp

You can do a lot of magic damage with the active ability of this item. Furthermore it adds some mana regeneration and ability power. This item works well, when you are able to use the active ability in a useful way. Otherwise you probably should not buy this item.

Guardian Angel

This item gives you magic resistance, armor and the passive revives you on death with a 5 minute cooldown. I think it is a pretty good item which gives you better survivability and the opponents might stop focusing you in team fights because of its passive.

Since I think it is not a good way to play Orianna full support, I do not go for Command: Protect in early game. So I head for Command: Attack and Command: Dissonance, which really helps your team a lot when played in a good way. Furthermore this two skills can also be used to take out whole creep waves as soon as you have enough mana regeneration.

First Spell

Flash

This spell is always good for escaping dangerous situations or chasing enemies, if the opponent has not many life left and you would not get him killed otherwise.

Second Spell

The second spell really depends on your team and your personal preference.

Exhaust

I really like Exhaust, because it is universally applicable. You can use it to attack in 1v1, in team fights to take out their main damage dealers, but also to escape from heroes chasing you.

Ghost, Clarity, Ignite

Ghost, Clarity or maybe also Ignite are other good options.

Check out bushes with your Command: Attack skill, before you enter them to be sure that noboby is waiting for you in the bush.

Use Command: Dissonance when you carry the ball to get a speed up in dangerous situations and to slow down chasers. If you do not have the ball, use your Command: Protect skill first to move it back to you.

For killing creep waves quickly use Command: Attack and Command: Dissonance together as soon as you have enough mana regeneration.

Orianna is definitely not a character you should start with, but if you like challenges try her out. The gameplay is somehow different from all other characters in League of Legends, because the skills are done by her ball, not directly by herself. She has quite low HP at the beginning, so you have to be a little bit more careful, do not underestimate that. However she is quite fun to play, I hope you enjoy playing her!