Edited 1/7/2011
-Updated items
-Added screen shots
-Made guide more unique
-Added tips on traps

Edited 1/8/2011
-Added Snap Trap tips
-Changed skill sequence

Edited 1/9/2011
-Changed masteries

Soon To Be Added:
-Snap Trap tips for middle lane
-Video footage

Caitlyn brings long range physical DPS to the field, allowing fleeing heroes to easily be 'sniped' off the map. Caitlyn allows other physical DPS champions to focus on the squishier champions as she attacks the further away enemies from afar. As with all heroes, there is not one way to build her and this is just a general way I found works.

NOTE: This is a "guide", meaning it is not written in stone. At the loading screen evaluate your enemy team, keeping in mind their summoner abilities. You will find that at one point it may be better to get an item that is not listed in this guide. Please do so, as this has only been written to "guide" you to success.

PLEASE NOTE: These are not the runes I currently use, and will be updated ASAP. For my current runes, see above, near the Masteries.

First off, I would like to state that if you are unaware of the difference between "Primary" and "Secondary" runes, than please read this before you continue. This does not only apply to Caitlyn, but every champion in the game.

X9Greater Mark of Desolation: (Provides +15 Armor Penetration) Armor Pen is important because this guide focuses on stacking Attack Damage. Also: Piltover Peacemaker (Q) and Ace in the Hole (R) both deal physical damage which is benefited by the Armor Pen.

X9Greater Seal of Replenishment: (Provides +16 Mana Regen / 5 at level 18) I take these as my Seals because it allows me to not put so much strain on my mana, which in the end, enables me to not purchase any sort of mana regeneration item. I feel that if you conserve your mana, than these seals will get you through the entire game no problem.

X9Greater Glyph of Celerity: (Provides +8.10% Cooldown at level 18) These runes can also be replaced. I find them helpful because they complement The Brutalizer allowing you to reach about 20% cooldown reduction at level 18.

X3Greater Quint of Desolation: (Provides +10 Armor Penetration) Same reasoning as Marks.

A standard 22/0/8 is applied to Caitlyn to allow maximum damage output.

Offense:
Deadliness: Increases overall damage output by increasing critical chance.
Archmage's Savvy: Allows access to next tier.
Sorcery: Further compliments The Brutalizer and the Greater Glyphs of Celerity taken, allowing for potential spam.
Alacrity: Boost to attack speed
Sunder: Compliments Greater Marks of Desolation, Greater Quints of Desolation, The Brutalizer, and The Black Cleaver potentially allowing an Armor Penetration of 91. Which will easily penetrate any non armor stacking hero.
Brute Force: Increased Damage.
Lethality: Increasing critical strike damage.
: 5% increase to ALL damage

Utility:
Perseverence: Increased regeneration.
Haste: Improved ghost.
Awareness: Increased experience gain.

The goal here is to allow Caitlyn to achieve maximum damage output, without building a glass cannon.
Doran's Blade Allows you lane for an extended period of time.

Health Potion Allows you lane for an extended period of time.

(Head to lane)

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B.F Sword Rushing this allows you to last hit creeps with ease and also greatly increases your harassing ability, by further scaling your passive and Piltover Peacemaker (Q) ability.

Berserkers Greaves These increase DPS by boosting your attack speed. Note: Boots are the #1 to change from game to game. If you notice the enemy team is full of Crowd Control spells, than it may be wise to purchase Mercury Treads. Think before you buy your boots.

The Black Cleaver This item further increases your damage and armor penetration.
Note: This item has been changed, but has not been updated by Mobafire. Its new stats are

55 Attack Damage
Attack Speed increased by 30%
Unique Passive - Shreds 15 armor per stack, has a maximum of 3 stacks. (Total Max of: 45 armor penetration)

These new stats increase your attack speed and require you to only attack your enemy three times to get the full armor penetrating effect

The Brutalizer This item compliments this build in so many ways. For the price you are paying, you are getting alot.
Note: I suggest that you do not upgrade it to Youmuus Ghostblade because other items should be prioritized first.

Phantom Dancer
Increases your attack speed which allows your Passive to proc more often. Critical strike change increases your DPS and improves your ability to last hit and tower push. The movement speed buff is needed as you previously took Berserk's Greeves, instead of swiftness.

Youmuu's Ghostblade
This item gives you a 4 second boost. Helpful for chasing, running, pushing towers or attack immobilized champions. Use this in combination with your Snap Trap to maximize damage.

Banshee's Veil This is your defense item, allowing you to block one spell every 30 seconds. That spell block can mean life or death, giving you crucial seconds to use flash and or ghost to escape danger.

Infinity Edge
Another crucial attack damage item. Syncs well with your Ghost Blade and Phantom Dancer, making your often occurring crits to deal more.

The Bloodthirster At this point, if you have a death play more cautiously and do not over extend, especially when an enemy is MIA. This item greatly increases your attack damage and lifesteal, but at the cost of loosing all bonuses on death.

After this point evaluate your situation and build what you think is correct.
Note: You can always drink elixars when your inventory is full.

At level 1 take Piltover Peacemaker to ensure damage and harrassing, followed by 90 Caliber Net and Yordle Snap Trap. After take Piltover Peacemaker whenever possible, only loosing priority to Ace in the Hole. After Piltover Peacemaker is maxed, begin alternating 90 Caliber Net and Yordle Snap Trap, taking your ultimate when possible.

Headshot:
Every 8 attacks (attacks while in brush count as 2), Caitlyn will fire a headshot, dealing either 150% damage to a champion or 250% damage to a minion.

This passive allows you to harass early game and deal exceptional damage when attacking the same target over a period of time. It is recommended that you use every head shot on the enemy champion to gain and sustain lane superiority. If you are not mid, than ensure that you are attacking from the bushes to increase the counter by 2 instead of 1.

Piltover Peacemaker:
Caitlyn revs up her rifle for 1 second to unleash a penetrating shot which deals physical damage (deals less damage to subsequent targets).

This is your primary ability used to deal damage, harass and kill. It is a skill shot, with about a 1.5 second charge up rate. Like most skill shots it can be shot over walls and trees allowing for unsuspected hits. The damage is modified by your physical damage, and synergies well with this build.

Yordle Snap Trap:
Caitlyn sets a trap to reveal sneaky yordles. When sprung, the trap immobilizes the champion and deals magic damage over 1.5 seconds.

This trap is good for protecting your flanks and snaring fleeing enemies. There is a setup time of about 1.5 seconds, so lead your fleeing target appropriately.

Note: These traps can be seen by the enemy and only give you vision when thrown.

90 Caliber Net:
Caitlyn fires a heavy net to slow her target, the recoil knocks Caitlyn back.

This ability has three uses: damage,slow,flash. The recoil allows Caitlyn to jump back a bit allowing for easy escapes.

Note: The recoil effect can be used to jump over small obstacles, such as middle's ramp. Generally speaking, you will not catch up to your running opponent if you are alone and hit them with this ability. The recoil offsets the enemies slowed movement speed. (much better when used with a chasing partner).

Ace in the Hole:
Caitlyn takes time to line up the perfect shot, dealing massive damage to a single target at a huge range. Enemy champions can intercept the bullet for their ally.

This ultimate has been seen in the original DOTA and other ports alike (HoN). It is a great finishing move, allowing your allies to take care of other priorities as the bullet takes path.

Note: Enemies can intercept the bullet from their allies. Also, if the target dies before getting hit, the cooldown will only be 5 seconds.

Note: These screen shots were taken from a practice game. Also: For time's sake, I picked Yordle Snap Trap as my second ability, however, it is recommended that you choose 90 Caliber Net.

A well placed Snap Trap can score you a kill or save you and your allies from an unsuspected gank. Note: You can only have 2 traps placed at once. Placing another will destroy the oldest trap.

Top Lane
Once you find yourself establishes lane dominance, it is generally a safe idea to place one of your two traps within this bush. The placement is key and it is vital to be inside the bush, as the enemy team will not have vision of it.
To ensure that the trap will be set off by either a gank from middle lane or a sneaky champion coming from their woods, place the trap around... (see next picture)

At the point that the trap is triggered, evaluate the situation in a standard fight or flight format. If you and your partner have the upper hand and there are little to no enemy M.I.A's than assault the target, otherwise, use this precious time to flee, allowing you to save your summoner spells for later.

If you find yourself on more of the pushing side, you want to not only have control on your bush, but also your enemies'. To ensure you will own their bush you must place a trap in there.

Placing a trap at the edge of their bush gives them minimum amount of time to react and allows you to spring an unexpected attack, usually resulting in a kill.

Overall, you should use movement prediction to approximative when your traps will be set. To achieve maximum damage, use your Piltover Peacemaker ability right before the enemy sets off your Snap Trap. This will allow you to channel the effect before the become immobilized, and use the time they are immobilized to auto attack them. Note: Do not use Piltover Peacemaker to early, or it will scare off your target

If you feel that you are an experienced enough player and can use Caitlyn's 90 Caliber Net to protect yourself, than disregard flash.
Flash: I take flash to allow myself to not depend on my 90 Caliber Net as a defensive skill. Caitlyn has no other escape mechanism, therefore requiring such to be efficient.

Ghost: This is the better of the two escapes, allowing for increased mobility. This can be used offensively or defensively alike. If I were to get rid of Flash, ensuring that I have ghost to save me.

Like always, summoner abilities are purely preference, that should compliment your play style and help cover your weaknesses.

Note: (This game took place on 1/7/2011)
Using this exact guide I headed to mid lane and got first blood within three minutes.

Here is my end stats.


Note: The build is a goal and priorities and changes should be made, according to your team and enemy team's lineup.

All and all Caitlyn brings a big gun to the field, providing her allies with long range support. Whether she is piercing armor, catching Yordles or sniping a headshot, she is a great addition to any team.

Please leave any comments, questions or concerns you have with this guide and I will respond ASAP. My in game name is "TripleX", feel free to add me and invite me to your games.

I hope you enjoyed my guide and I hope to see you on the field.