Wow. Shen. Shen, since the buff UBERBUFF, Shen has been an absolute terror to play. And I don't mean terror for people playing him, I mean a terror to those facing him. So Riot "nerfed" him. A base armor reduction of 4, a Vorpal Blade heal reduced from 2% to 1.5%, and a Feint cost increase of 10 and level 5 nerf of 20HP. Honestly, none of these made a real impact into my gameplay of Shen. But I digress, my purpose here is not to tell Riot to nerf Shen again (I would prefer that they did not), but to point out how amazing he is in a large variety of roles at the moment. It is quite likely that this guide will quickly become outdated as Riot "balances" Shen, but I will attempt to keep it current.
A quick mention of thanks as we move on to the build:

Jhoijhoi, for her amazing guide on guiding guides which can be found here
Chubby Baby and giantzombie (again), for their suggestions and other help.
Also Riot, for buffing the **** out of Shen

And now, without further dissembling, the doctor is in.

Create a jungling guide
Test Shen mid more

PROS:

*Shen has amazing sustain in lane
*Shen has a global presence
*Is EXTREMELY durable, with high early-game damage
*Has a no cost, low-cooldown, high-shield, champion-targetting ultimate.

CONS:

*Can be very energy-hungry if not played intelligently
*Drops off slightly late game
*Can be difficult to farm with
*Countered fairly hard by some champions

Jungling Msteries
I dislike Shen's Jungling masteries. Why? Because there are so many options! 9-21-0, another 9-21-0, 0-30-0, and 0-21-9! It is simply maddening, but it means you can suit your playstyle and available runes.
9-21-0(the first) Is 2 points in Brute Force and Butcher , and 4 in Alacrity to get Void Stone. 9-21-0 (the second) Involves the same starting point, but getting 4 in Sorcery to get Arcane Knowledge . 0-30-0 gets everything but Resistance and Vigor , however, you can get Resistance if you dislike Mercenary . The 0-21-9 tree is difficult, as Shen does not use mana, nor will you die often as the Jungler/tank. If I am taking Flash or Clairvoyance, I may take Summoner's Insight , or might just take Expanded Mind and Improved Recall . However, Improved Recall is MUCH better for laning, so the whole first row (in my opinion) is rubbish for Jungling Shen. Then 4 points in Swiftness (or 3, and 1 in Scout ), and take Runic Affinity . The choice is yours, there are certainly enough options!

Runes on Shen are almost unnecessary. I prefer this setup for early durability, but you can go with almost anything (although I really do prefer greater quintessence of vigor over any other Quint.

GLYPHS
With Glyphs, you may want to switch to 9 Greater Glyph of Scaling Cooldown Reduction or Greater Glyph of Cooldown Reduction (they break even around level 13). You could even get 9 Greater Glyph of Energy or Greater Glyph of Scaling Ability Power. Each has its benefits and drawbacks, so it is up to you.

MARKS
I like MPen Marks on Shen. If you really want AD or anything else, I guess that's up to you, but I recommend against it. You are a tank, anyways. Marks probably won't turn out well for you.

SEALS
You have a LOT of leeway here. Bonus flat health, flat HP regen, energy regen flats or per levels- I only use armor because it is convenient.

greater quintessence of vigor QUINTS
As with marks, I much prefer one kind: HP Regen flats. Early game sustain is king while playing Shen. I suppose you could also take HP flats for the bonus... 72-76 HP, but I advise against it.


Jungling

Runes for Jungling are almost as adaptable, the only requirement is 9 Greater Seal of Armor, and even that is flexible depending on how you do it. Flat health in Quints, Mpen in Marks, and CDR in Glyphs is what I personally use.

Early Game

Start off by taking a Doran's Shield. Not much else will suffice for our purposes. The shield provides armor, health for your Ki Strike and Vorpal Blade, and extra HP regen for your sustain. After this, either pick up your Boots or Heart of Gold. Try to return when you have enough for both (1175GP). Finish off your Mercury's Treads (or Ninja Tabi if there is little AP/CC on the enemy team), and build an Aegis of the Legion. Which parts of the Aegis of the Legion you get first depends on money and the lane you are in. Do you want more health? Ruby Crystal. MR? Null-Magic Mantle. Armor? Cloth Armor. If money does not allow for what you want, just buy whatever you can. DO NOT FORGET TO BUY WARDS. Either in mid or solo top, you will want to be pushed and harassing the enemy out of lane. This gives you a big lane presence, and people will call for ganks more. If you are against a duo top lane, this obviously doesn't apply.

Mid/Late Game/Situational

Here's where your build becomes completely situational. Take a look at the enemy team. How many ADs and APs are there? Who is getting fed? Are you dominating? Maybe you want to grab an early Rylai's Crystal Scepter. Has that jungling Tryndamere gone from 0-1-0 to 2-1-1? Maybe think about getting extra armor. Malzahar been tearing up mid? Maybe an early Force of Nature. In this section, I will discuss different items and their uses.

When People are Hitting you too Much (Against AD)

Frozen Heart
A very good item, gives 99 armor and the 20% AS reduction is great. HOWEVER: Only stacks ONCE, so no point in having two on the team AND you waste 500 mana by taking it. Good against AS champs (Ex. Vayne, Teemo, Kayle).

Locket of the Iron Solari
Definetly a great item, adding sustain, armor, health, and a shield for very cheap. So close to going into the actual build, except it doesn't provide any MR and drops off late game. In a game with little AP on the enemy team however, it may be worth it to purchase this instead of your Aegis.

Randuin's Omen
Amazing armor, good HP, and a great teamfighting Active Effect. Just remember to use it.

Sunfire Aegis
Not a HUGE fan, but it provides many benefits like HP, armor, and the 35DPS. That may not seem like much, but it adds up over team fights and helps farming.

Thornmail
Only against very heavy/super fed AD ( Tryndamere, Vayne, Master Yi). That said, it is godly against them.

When You're Being Zapped to Death (Against AP)

Abyssal Mask
Nice amount of AP and MR. Works well in a variety of situations, but not usually included in my build. You sacrifice too much tankiness.

Banshee's Veil
Generally not a great choice on a tank, unless that one CC is screwing you over big time. Better on squishies and carries.

Force of Nature
Yes. 76 MR and that godly passive which synergises extremely well with your high HP.

Quicksilver Sash
I love this item. I almost never use it, but I love it. 56 MR and a cleanse, all for only 1400GP? You can buy this without blinking an eye.

Spirit Visage
Maybe, if you need more sustainability. Provides CDR, HP, and MR as well. For only 1550, it is a definite candidate for early game items, especially if you are getting harassed.

When Everyone is Fed (All-Around)

Guardian Angel
No. Just no. Under almost no circumstance should you take a Guardian Angel on a pure tank. The idea is to get people to focus you, not have them avoid you because you're just TOO tanky. Also, the idea is to be first AND LAST in the fight, and if they manage to catch you and your teammates are dead/running... Well, there goes the passive. It does give nice stats as well though. THIS WORKS ON SHEN. If you have had a very good game, and are hurting people a lot with ganks, you will likely be focused by some people in team fights. It give buttloads of Armor and MR, and can be very nice in certain situations.

Leviathan
MMMMM.... But no. Maybe you ARE getting fed on assists/kills soloing top/mid, but then you will worry about losing your stacks and play less aggressively, including in team fights. Also, it requires a lot of stacks to be worth it. However, if you manage to reach 20 stacks.... But don't. Unless trolling or otherwise.

Shurelya's Battlesong
Ehhh... Good HP, and regen, but wasted MP regen. The CDR is nice, but not at all necessary, and you don't really need movement speed boosts.

Soul Shroud
Good HP and CDR, but wasted mana regen. For 2285, it's not very cost-effective.

Warmog's Armor
Wow. HUGE shot in the arm for HP, boosting your Ki Strike and Vorpal Blade. However, it is expensive, and should mainly be used against very high-burst teams ( Talon, Brand, Akali, etc.).

When You Want to Kick Some *** (Offensive)

Atma's Impaler
Definitely better on offtanks, but you would be getting a LOT of extra AD (80 at 4000HP). You get armor and crit chance as well, but I would still advise against it (I prefer HP on Shen).

Hexdrinker
AD, MR, a shield... What's not to like? But again, I prefer AP. Whatever floats your boat, I guess!

Lich Bane
MR, AP, a bit of wasted mana, movement speed, extra damage on hit? Definitely not a bad idea. Especially if you're stacking other AP/MR/Armor/HP items.

Madred's Bloodrazor
Similar to Atma's Impaler, provides a bit of defense and a lot of offense. For 3800, it provides very little survivability, but your Ki Strike will proc more often and you will deal tons of damage.

Moonflair Spellblade
Not used enough, in my opinion. A fair bit of AP (75HP for your shield) and tenacity? Sounds pretty good, especially if you didn't grab Mercury's Treads.

Nashor's Tooth
No defense, but AS, AP, CDR.... This can make you VERY dangerous, but you will lack survivability.

Rabadon's Deathcap
Wow. Lotta AP in this section. Zhonya's Hourglass, Abyssal Mask, Lich Bane.... Looks like I've got the makings of an AP Shen tank build.... Hmmm...

Sorcerer's Shoes
A definite option, but no defense whatsoever.

Void Staff
Probably not, unless you have pretty much every other AP item in this section.

Wit's End
Boosts your AS, MR, and increases your damage? Not a bad item, worth picking up in some cases more than in others.

zeke's herald
Considering it gives survivability, CDR, AND a team buffing aura while you're in the middle of the fight, this is a great choice if you have a fairly heavy AD team.

Zhonya's Hourglass
If you're going AP, GET THIS. A bunch of extra armor, great AP, and an awesome active. Dive into the fight, tear some **** up, pop this to confuse them, and two seconds later you have more energy, shorter cooldowns, more health, and generally become a problem. Plus, that golden statue is distracting as heck.

Force of Nature Vs. Rylai's Crystal Scepter
Both items provide health, offense, and a slow. It is mostly up to you, and how you are building, but it is generally a good idea to include at least one of these in your build.
Frozen Mallet provides slightly more health, gives AD, and the slow procs on basic attacks. This will probably end up activating more in a fight than a Rylai's Crystal Scepter proc.
However, Rylai's Crystal Scepter will scale with all of your abilities, and you will gain a slow with your Vorpal Blade (and somewhat with your Shadow Dash). It's just as good for chasing as Frozen Mallet, if not slightly better.
In the end, it's up to you and your build. If you've taken Atma's Impaler, zeke's herald, etc, then go with Frozen Mallet. If you have Zhonya's Hourglass, Lich Bane, etc, go with Rylai's Crystal Scepter.

This section is more on what abilities do. More on how to use them later.

Ki Strike
I never understood this ability at first; it seemed like a useless passive for a tank. With my current Shen playstyle however, it is one of the staples of my combo. Whenever it goes off, you deal bonus damage equal to (4+6xlevel+10% of bonus health). Early on, that's not too much, but is still substantial, especially once you have a Heart of Gold. It restores (10-20-30) energy which is somewhat helpful. At level one, that's equal to one second of natural regen.

Vorpal Blade
This ability is an amazing EVERYTHING. It heals you, damages opponents, is a ranged harass, and is EXTREMELY SPAMMABLE and low cost. The heal also scales on 1.5% of you MAXIMUM health. It is a very large ratio, even though it may not seem like it, especially on a 5 second status effect. That's worth 7 seconds of heal, which is (at 1000HP) 105 HP, not including Vorpal Blade's base stats.

Feint
Early game, the 70HP this shield provides is amazing. The anti-harass is amazing in lane. This ability drops off late game, but we still want the initial boost at level four.

Shadow Dash
This is your bread and butter as Shen. It provides a flash, taunt, wall-jumper, gap-closer, damage reducer, etc. I honestly don't think that I need to explain too much as this skill is pretty self-explanatory. It is extremely high-cost though, so try to hit champions to reduce the drain. One last thing I want to point it is that you can Shadow Dash to close a gap and toss a Vorpal Blade to finish off a runner, then return to the lane/fight.

Stand United
Lane return, shield, courage-enhancer, fear-inducer, life-saver, gank-enabler... Are you seeing a trend here? All of Shen's skills have multi-use ability and much utility. In particular, use your ult on a squishy in a team fight, to help gank bottom lane, etc. Since you gain more exp as solo top, 250HP when bottom lane is probably level 4-5 is no mean feat. 850HP at level 16? Nice. Mid just got ganked and is being turret dived? Stand United, Shadow Dash, Vorpal Blade- BAM! Double kill. I have one thing to say about this ultimate though. It can be very difficult to focus on harassing your lane and keeping your map awareness up. Map awareness is key when using Shen in this way. The only advice I can give here is practice, practice, practice.

I take Shadow Dash first because it is invaluable right from the get-go. Either to escape, gain distance, strike fear into the enemies, or start harassing before you even hit level two. We take Vorpal Blade second because it give amazing harass, sustain, and is one of our favorite Shen skills. The three early on points help amazingly with your general gameplay. We take Feint early as well because the extra 70HP of shield for 50 Energy is a very good prevention of the enemy harass (especially while taunting them), and saves some of your Vorpal Blades for harass rather than sustain. From here it is extremely simple, prioritizing Stand United > Vorpal Blade > Shadow Dash > Feint

Optimal

Heal or Flash
Ah, Heal. Such a great spell. Great for baiting (I hear that it's a master at that), helping carries in team fights, sustain, etc. Flash as well is simply amazing, especially when you want that Flash+ Shadow Dance for escaping or initiating, or just Flashing when you run out of energy. I suppose you could take something else, but these are preferred.

Teleport
A ninja never walks. Unless, of course, he wants to. This spell offers about 99.9% less utility to other people than it does to Shen. For example: You are in top lane. Bottom lane is getting triple ganked, many people are low. You ult in, provide the carry a shield. Shadow Dash, Vorpal Blade, etc. 1-2 of them drop, and you may chase down the third. Now, maybe your top oppenent has realized it is his/her chance to push. Simply back, buy with your new money, and Teleport. It is essential to maintaining global dominance as Shen.

Viable

Ignite
Only if no one else has it. The only real good use for your Ignite is to use it on the highest life-gaining person on their team in a team fight (ex. doctor mundo, lifesteal Tryndamere, Volibear).

Exhaust
See ignite. Only difference is use it on the most deadly enemy.

Clairvoyance
Maybe. Avoid it, unless you can use it really well.

Just Don't.

Surge, Promote, Clarity (wtf?), Ghost, Revive, Cleanse

I would explain all of these (as I did in my Skarner build), but it should be obvious. If you have any questions or discrepancies, please comment.

Jungle

Smite
For jungling.

Your second spell can be Heal, Flash, Ignite, or Clairvoyance, depending on your playstyle and what your team needs. I usually take Flash or Heal, as both help tremendously in ganks/late game.

Ahhhhhhhh. Solo top Shen. The greatest thing since... Well, ever. Against one person? Great. Against two people? Even better! You do not have to worry about being ganked, you just have to play more strategically. Let's make a list of steps here. Assuming an average lane(against another solo top), this is how it should go:

Enter lane (try to enter the bush first)
Wait for minions (fairly important)
When the enemy goes to farm, Shadow Dash them, Ki Strike, and maybe add a few more autoattacks, then walk away. You are not an early game duel champ. You are a ninja, here to beat the **** out of your opponent before they know what's happened.
Once you hit level two, just add Vorpal Blade to the mix. Shadow Dash, Ki Strike, Vorpal Blade.
At level four, it should become: Shadow Dash, Feint, Ki Strike, Vorpal Blade in no real order. Whatever works up for you.
Don't forget that you can spam harass Vorpal Blades from a range, making almost any lane matchup easier.
Sustain with Vorpal Blade if you need to.
BE CAREFUL FOR GANKS. Get wards ASAP, and try to avoid pushing your lane to hard. By harassing the enemy out of lane, you will be putting a big red X on your back.
Don't forget to farm. You may not need it as much as a carry, but it will allow you to buy items faster, increasing your tankiness, increasing your damage/burst, your sustain, global prescence, etc. Both Ki Strike and Vorpal Blade are amazing farming tools.

Against two people, the main changes are:

Try to taunt both if you can.
Only harass one at a time.
Try to focus a squishy.
Unless you have pushed both out of lane, you may want to Teleport back into lane after you recall.
The great thing about being against a duo lane is that you will usually be A) overlevelled and B) pushed up to your turret. This means that you will be able to sustain with your Vorpal Blade under the safety of your turret.

Mid Shen is much like solo top, but easier in some ways and harder in others. For one, DO NOT MID Shen IF YOU HAVE LAG. You NEED to dodge most (or some) of the skillshots thrown at you. You DO have lane sustain, however (probably more than your opponent), but avoid taking damage. Overextending in mid is very dangerous, especially if your opponent has a hard CC - in this situation, you should almost never extend past half. If you can, you should play aggressively and harass, but this may not always be best if your opponent can just beat down on you after your taunt ends (against Swain or Ryze for example, as they can both stop you from moving after your harass and then return it). In this case, just use Vorpal Blade to harass and Feint to prevent theirs. You may need to take an extra point or two in Feint early on if you're against a harass heavy lane, and conserve Vorpal Blades for healing rather than harass. Also remember, you can do any other lane, so if you REALLY need a swap, just ask your team. Other than that, mid Shen is very simple.

Jungling Shen is very difficult fairly easy in my opinion. He has a very slow moderate jungle time, and each time you gank draws heavily a fair bit on that, (however getting kills in those ganks is easy). I'm currently testing different routes, masteries, and starting builds, but it seems that this may take a lot of work. So far though, I start off with either Cloth Armor and five Health Potions or a Ruby Crystal. I prefer the Ruby Crystal because it can be built right away into a Heart of Gold or Aegis of the Legion. It synergises well with both Vorpal Blade and Ki Strike. Ideally you want to get Ninja Tabi early on as well, however, if there just isn't enough AD on their team (or their team is Warwick, mlzahar, Alistar, Leona, and Annie), stick with Mercury's Treads. Take Vorpal Blade first and start at either Red or Blue (get a leash)(Possibly get Wolves/Wraiths first). Take Feint second, spamming both on every camp, clearing the jungle until you hit level 4, and take your Shadow Dash for ganks. You can either gank or continue clearing at this point, but try to ungle as much and as fast as you can.
The basic skill order is QWQE, then whatever you really need (prioritizing Q).
A general order for me is:
Wolves
Blue
Wraiths
Wolves
Possible gank
Wolves or Wraiths if either is up, if not then:
Golems
Wraiths
Red
Wolves
Ideally, you want to be level 4 before you gank. That Shadow Dash is NECESSARY.

It is my firm belief that Shen is one of the strongest champions currently in the game. My efforts in this guide were made simply out of an urge to show this to you, my dear Summoners. Whether or not this guide has helped you, I wish you good luck, and thank you for reading. :)

Oct 22,2012
Fixed a few errors and typos, added in my somehow-overlooked Flash spell (wtf, Junksie?)
Sept 22, 2012
Reviewed for Syndra patch
August 11, 2012
Reviewed for Diana patch
May 21, 2012
Changed/finished Jungle guide
Reviewed guide for Varus patch
Changed opinion on Guardian Angel
March 15, 2012
Added Mid
Started on Jungle
February 27, 2012
Posted build