Diana is a very versitle AP melee champion. This guide is for laning in Summoner's Rift but will cover modifications for jungling. It is effective in all 3 lane positions. With this build, you should be able to harass, assasinate, scout, and with Flash, even dive successfully.

Play in the Twisted Treeline and the Crystal Scar will be added in seperate tabs as there are items available in those arenas that modify the build significantly.

While reading my guide, I would also like to suggest a listening guide as well. There is a common theme and they are available on iTunes and elsewhere:
Diana - Paul Anka
Dirty Diana - Michael Jackson
Diana - The Sounds
Diana - Nerf Herder
Diana - Waterdeep
Diana - Alexander "Skip" Spence
Diana - Earth, Wind and Fire

I prefer scaling runes to flat runes as overall you get more out of them. Flat runes give you an early edge, trading for less of an advantage later on. Please feel free to substitute for your own personal preferences.

Greater Mark of Attack Speed - Attack speed will make farming easier and cause your passive to trigger more often.

Greater Seal of Defense - You will need some armor, but not a huge amount early on and you will get additional armor as well as minion damage resistance from Masteries. This will be enough to give you survivabilty in early team fights.

Greater Glyph of Scaling Ability Power - AP glyphs for increased damage.

Greater Quintessence of Scaling Ability Power - More AP.

I go with a 21/9/0 breakout.
Offense:
Mental Force , Blast and Archmage for AP.
Fury for an attack speed boost and Spellsword for a straight up damage boost to your normal attack.
Arcane Knowledge for magic pen.
Executioner for additional damage on low heath opponents.
Butcher for extra damage to minons and Destruction for improving damage to towers.

You will spend most of your time beating on minions so Butcher will have an advantage there (also when jungling) and Destruction when you go for towers (it also makes for faster back dooring).

A couple of alternitves in the Offense tree is to put the 2 points from Butcher and 1 point from Destruction into Sorcery for a 3% boost to your cooldown rate or into Havoc for additional damage. Also if using Ignite, Exhaust or Ghost one point could be moved to Summoner's Wrath .

Defense:
Resistance for magic resist.
Hardiness for a slight armor boost.
Durability and Veteran's Scars for extra starting HP.

There is not much room for substitution on the Defense tree.

Utility:
I normally take nothing under the Utility tree but you can use the point reserved for Veteran's Scars in the Defense tree could be used her for Summoner's Insight to improve the cast time of Teleport and the cooldown of Flash, but I think you get more bang for the point when used for Veteran's Scars .

I use Teleport and Flash for maximum mobility. Other options include replacing Teleport with Ignite for additional damage, Smite if you are jungling, and Ghost for either chasing or retreating.

Other spells may also be useful, here are my thoughts:
Exhaust: Useful for slowing enemies but since you have a teleport ability its usefulness is limited to allowing allies to catch up or for you to get away, but Flash is better for getting away.
Heal: A generally useful summoner spell.
Barrier: Useful but redundant since you already have a skill that does the same thing with a much lower cooldown.
Revive: Limited utility early game, but can be useful late game at cutting down dead time. I still feel that there are better choices.
Cleanse: Useful in a very high debuff enviroment, but useless otherwise. It is a gamble in anything other than ranked play and I prefer more solid effects.
Clarity: Not really useful except the first 10 to 15 min of the game. Once you have built Athene's Unholy Grail you generally will not have mana regen issues.
Clairvoyance: Exceptionally useful for a sudden quick check of an area of the battlefield, beyond that, use wards as they are much more effective and last longer.

To start I recommend an Amplifying Tome and a Mana Potion. This will give you an AP boost and hang time in lane. Quickly upgrade the Amplifying Tome to a Fiendish Codex. This will further increase AP, add some cooldown for your spells and mana regen. Next build a Chalice of Harmony, then Athene's Unholy Grail for AP, magic resist, mana regen and a cooldown boost. You should have very few instances where you are lacking mana once you complete the Grail.

Next build boots, I use Ninja Tabi for armor. I have also used Mercury's Treads in a heavy stun/slow enviroment and Sorcerer's Shoes for those few times I need magic pen. If I am packing Teleport and Flash, I will take Enchantment: Distortion for the better cooldown on my summoer spells or if I need extra movement speed Enchantment: Alacrity.

The third item should be Nashor's Tooth to increase AP and attack speed. This will also max out your cooldown percentage. I prefer to start with the Fiendish Codex, then build the Stinger, and then upgrade, but it can be done in any order.

Your fourth and fifth items should be Rylai's Crystal Scepter and Liandry's Torment. Go Rylai's Crystal Scepter first for more HP or Liandry's Torment if you need magic pen. This will give you AP, a huge health boost a slow and a damage over time effect that has a double effect on a slowed target.

Lastly, build Rabadon's Deathcap for a massive AP hike.

Alternative items:
If you want to go with an armor build instead of HP, replace the Liandry's Torment with a Seeker's Armguard early and then Zhonya's Hourglass mid to late game. The Rylai's Crystal Scepter should be replaced with an Iceborn Gauntlet. The cooldown reduction will be lost because you will max at 40% from Athene's Unholy Grail and Nashor's Tooth.

An Abyssal Mask can be built for AP, more magic resist and additional lowering of opponent magic resist, replacing preferably the Liandry's Torment but the Rylai's Crystal Scepter can be replaced instead.

You can grab some additional attack speed and damage from Malady, on hit effect from Lich Bane and Morellonomicon, or an AP and huge mana boost from a Seraph's Embrace with a slightly redundant shield effect.

Crescent Strike [Q]: Main damage dealing spell, AoE, and start of her primary combo.

Pale Cascade [W]: Damage shield and secondary damage spell that will hit multiple targets if close together. Very useful in team fights (in concert with [E]) and against minion hordes.

Moonfall [E]: Grab and slow ability. Much more useful late game for team fights as is an effective stun while enemies are being pulled towards you and then they are slowed.

Lunar Rush (Ultimate) [R]: Teleport to a champ and deal damage. If under the Moonlight effect from Crescent Strike [Q] then cooldown resets almost immediately, allowing for a second strike at the same or a different target.

Start out with Crescent Strike as this is Diana's primary damage dealing spell. Alternate between it and Pale Cascade until level 6. Take Lunar Rush at level 6, 11 and 16. At level 7 take your first level in Moonfall as there will not be much opportunity to make it useful before then. Max Crescent Strike by taking it at level 8 and 9. At 10, 12 and 13 take Pale Cascade to max it out and then level Moonfall from there.

You could take the first rank of Moonfall at level 5 and then rank 3 of Crescent Strike at level 7, if you find yourself wanting/needing it earlier.

General: First of all, Crescent Strike is great for checking bushes for hidden champions and if it connects, then it will breifly illuminate them with Moonlight. It is a great way to keep tabs on the bushes early game. Secondly, you have a decent reach with Crescent Strike so smack the caster minions with it while you are beating on the melee minions. Grab the blue buff early if there is not another caster or jungler that needs it.

Top: You can solo top better when you are on the purple team since the natural arc of Crescent Strike allows you to check the whole bush closest to the turret. When solo, you will have difficulties with ranged opponents until you can get either Lunar Rush or some mana regen and cooldown so that you can cast Crescent Strike more often.

Mid: For a melee champion Diana is an excellent mid. Crescent Strike is a solid ranged attack and has a high enough damage to make things difficult for anyone that doesn't have good magic resist or high HP at start. When pushing the turret, Crescent Strike allows you to stay out of range, but still do damage. To a certain extent, it removes the safety of sitting under the turret with low health as you can strike and then pull out of turret range before it fires. Again, you may have difficulties with ranged champs but is less of a handicap mid since you have more room to move around.

Bottom: You shine best when on the bottom of blue team for the same reason you solo top better on the purple side, the arc of Crescent Strike matches that of the closest bush.

Season 3 changes the build for jungling majorly. Start with a Hunter's Machete and quickly upgrade to a Spirit Stone and then build a Hextech Revolver and then purchase Spirit of the Spectral Wraith as quickly as possible. Then proceed with the normal build, selling Spirit of the Spectral Wraith when you go to build Rabadon's Deathcap.

Another potential starting item is a Wriggle's Lantern as it builds from Hunter's Machete as well but Diana does not benefit from the AD, armor and lifsteal as much.

Teleport can be replaced with Smite for jungling. I do not recommend replacing Flash.

When jungling, I usually start at either wolves or wraiths. Get the blue buff at level 2 and you should be able to solo the Golem with 1 rank in Crescent Strike and Pale Cascade. Lead into each creep camp with Crescent Strike and then activate Pale Cascade as you move in to melee. If you have Lunar Rush then you can use that to jump to a creep after activating Pale Cascade and while the creep is still touched by Moonlight. This will do additional damage as well as reset Lunar Rush's cooldown.

Diana should be able to solo the Dragon once you have Athene's Unholy Grail and at least another Fiendish Codex. Use her main combo of Crescent Strike, Pale Cascade, Lunar Rush. Even though Lunar Rush's cooldown will reset when you hit the Dragon while it still has Moonlight from Crescent Strike, resist using Lunar Rush the second time. Wait until you are going for a killing blow or the cooldown will be much longer for very little gain.

Diana is an excellent farmer as Crescent Strike has a good attack area and with Moonsilver Blade also makes for good farming since every 3rd strike hits multiple targets if they are in close proximity. Pale Cascade can damage large numbers of minions quickly as well as provide a damage absorbing shield and when combined with her Moonsilver Blade allows efficent clearing of minion waves.

Pro: You will have a very high amount of AP. Pro: Opposing champions will need to build a very high level of magic resist to prevent damage so that means less offensive capablity on their end. Pro: You are very effective up close and personal. Pro: Your skill combo (QWRR) is extremely effective at dealing damage and letting you get to your target.

Con: While not a glass cannon you are a ceramic cannon, a bit sturdier, but still fragile and will break. Con: This levels the playing field since you will have lower levels of armor/magic resist as a trade off for high AP. Con: You will have issues with some ranged champs until the cooldown on Crescent Strike goes down or you get Lunar Rush. Con: It all depends on your landing a shot with your [Q] to start it off.

This build has not been tested in ranked play and I would appreciate feedback from other players on it so I may expand this section, since I do not play ranked.

This is a very effective build once you learn how to use it. It tends to need to be played more as you would a ranged or commando champ at first (i.e. keep your distance and/or hit and run) but later you can get into the thick of it. I consistantly achieve 2 to 1 and higher KD ratios.

Please comment and let me know your experiences using this guide. I am always looking for alternitives to the play style and ways to improve. Criticism is certainly welcome, but please make it constructive and don't just tell me "It sucks" without providing a reason or suggesting a way to modify it so it sucks less for you.

Thank you for reading,
Typhon Grey

***A special "Thank you" to jhoijhoi for her How to Make a Guide guide.***
***Another special "Thank you" to Ibcsi for indirectly pointing me in that direction.

Ver. 1.05 - Item updates and typo corrections.
Ver. 1.04 - Massive update for Pre-Season 3.
Ver. 1.03 - Added Laning Stratagies section, color changes, editing and few typo and coding corrections.
Ver. 1.02 - Added listening guide and reorganized Pros/Cons section.
Ver. 1.01 - Added graphics for masteries, item builds and skill selection.
Ver. 1.00 - Base guide.