Welcome reader,

This is a guide to the defensive tab. That button right there in the shop. It will discuss general hints, counterplay options, and discuss specific items.

Understanding these subjects is vital to learning about counterplay, and learning about how to build durable, cost-efficiently.

So let's get started!

Efffective health, or EHP, is a term often used by players to summarize ALL your defensive stats. The idea behind it is that if you buy resistances that give you 50% damage reduction, then this equates to doubling your health.

A formula you can use is EHP = Health x (1+Armor/100). Defence against magic damage can be described by the same formula, but with changing armor by magic resistance.

An alternative way of looking at it is saying you want to multiply the time you survive combat. Doing this can be done by looking at how buying a defensive stat increases your survivability. Damage is calculated using damage received = (damage)*100/(100+armor) (or magic resistance). In other words, if you want to survive 2ce as long, you could double your health, or increase your damage reduction.

The consequences
What the above reasonings imply is that defensive stats become relatively less cost-efficient as you buy more. The exception to this rule was dodge, which is ppb one of the reasons for it's removal. If you have 0 armor and buy 100, the incoming physical damage will be halved! Though if you buy another 100 armor (adding up to 200), this armor will multiply the incoming damage by 0.67 instead of by 0.5. It might have been better to buy health!

I've made a graph to explain this using the EHP point of view too:
As you can see, for a fixed amount of health the amount of EHP you get from buying defensive stats increases linearly with said defensive stats. However, buying health increases the slope of the function. It boils down to this: armor and magic resistance add a fixed percentage of your health to your EHP. Buying more armor and MR thus gives you bonus EHP. However, there comes a point where the EHP you get from the extra scaling buying new health gives you outweighs the EHP you get from buying more resistances. This is why it's not cost-efficient to keep buying resistances. Buying only raw health is also bad because the EHP you get from resistances is initially more gold-efficient than raw health. Morale of the story: always try to get a mix of both!

This depends on a couple of factors:

- Your role in the team.

• As AD carry, it's generally best to invest in allround pure damage due to damage multiplication being pretty high in LoL. It is however common to pick 1 (maximum 2) solid all-round defensive items Think Banshee's Veil or Guardian Angel. Staying alive as the highest damage dealer on a team is important!
• As AP carry, you don't have to buy pure defensive items! There are many items that offer both AP AND good defensive stats ( Abyssal Mask, Rod of Ages, Rylai's Crystal Scepter, Zhonya's Hourglass,...)
• As support, you'll want relatively cheap defensive items that benefit your team. Maybe aura items like Aegis of the Legion or Abyssal Mask.
• As offtank, tank or bruiser, you'll need more. Read more of this guide :p.

- Your opponents

• If an ennemy team is based around 1 type of damage, counterplay to it by buying armor or magic resistance accordingly
• Extending the last point, keep an eye on which ennemies are potentially getting fed.
• Certain items hardcounter certain champions/teamcomps (most notibly: Quicksilver Sash against Mordekaiser, Malzahar, Warwick,...)

- Your champion and team setup

• As carry, the more frontliners you have on your team, the more you can ignore defensive items.
• The higher your base damage, the more you can afford to farm up for those expensive defensive items. (Mainly applies to bruisers, who tend to go for balanced setups in all stats)
• As frontliner, the less frontlining allies you have, the more you MUST build defensive.

Health directly effects your EHP. This is a GREAT stat!
The only counter to buying health is damage based on the percentage of the ennemy's maximum health ( Silver Bolts, Bio-Arcane Barrage, Madred's Bloodrazor, Blaze...).

Doran's Shield, Doran's Ring and Doran's Blade: These items are great starting items, and great to get back into a game when you're behind. They give you 80 - 120 raw health, which is great as defence, as well as some bonus stats. Overall great items in the early and midgame. They fall off later.

Catalyst the Protector: Insane sustaining item. Get this on mana-hungry casters.

Frozen Mallet: Great item on offtanks. The added damage bonus is quite small, but you should get it mainly for the health and the passive slow bonus. This item is a staple item for many bruiser champions.

Haunting Guise: Situational for when you as a mage need a general stat boost. Good on champions that aren't mana hungry, or NEED kills.

Heart of Gold: Magnificent item. This item is a staple item for supports, tanks, bruisers and offtanks. If you buy it early, it is almost always worth it's gold cost!

Leviathan: If you like stacking items. NOT a fan of it. NEVER buy this to counter ennemies. Rubbish for the most.

Rod of Ages and Rylai's Crystal Scepter: I'll mention them together. They are the equivalents of Frozen Mallet for mages. Both great items. Worth combining if you don't have decent frontliners. These items will give your AP carries an overall stat boost.

Warmog's Armor: The classic health item. Big chunk of health, but the disadvantage is you need a lot of farm to get it working. Buy this if you know you're in a stable lane where you can get a lot of farm. If you're getting your arse kicked in lane, don't bother. Get gp5 items, doran's items and Frozen Mallet instead. If you buy it, try to buy it early for maximum effectiveness.

Atma's Impaler: Insanely cost-efficient item. It synergises well with items that increase your health significantly, like Warmog's Armor and Frozen Mallet. Good on bruisers. Don't get this as carry!

Ninja Tabi: Cheap and easy way to obtain some more armor. The inherent damage reduction is stronger than often given credit for, because it's a non-armor damage reduction source. As already discussed, enlarging the amount of different sources of survivability is the most efficient way to build defensively in LoL.
Buy this item if you are melee, your laning opponent deals physical damage, AND the ennemy jungler deals physical damage. NEVER buy this on any ranged AD carry except Urgot, any mage or any support unless at least 4 ennemies deal almost exclusively physical damage.

Frozen Heart: This item gives you high armor, cdr and mana; as well as an aura. Make sure that the champion you buy this on benefits from all these stats, and is preferrably melee. Champions that come to mind are Singed, Blitzcrank and Ryze.

Randuin's Omen: This item hardcounters melee ennemies. It builds from Heart of Gold and Warden's Mail, which are formidable items in their own. It punishes ennemies for attacking you. The active rocks as well. This item, or just Warden's Mail, is a superb countering item against melee champions. The fact that it gives both armor AND health makes it allround awesome. Cdr is a nice bonus, but don't buy this just for that.
When playing against an ennemy with this item, don't auto-attack him unless you have an on-hit effect like Pulverize ready. Try to rely on skill damage rather than auto-attacks, unless you have a killing strike ready.

Sunfire Aegis: Not much of a countering item, but great on tanky melee champions. Synergises with champions that hug ennemies anyway. ( Garen, Renekton.)

Thornmail: Relatively cheap, counteritem n1 against attack-speed based ennemies (disreguarding on-hit effect nuisances like Kog'Maw and Teemo). Buy this against a strong ennemy Master Yi, Ashe, Tristana, Vayne,... Generally good against ranged AD carries. Strong counteritem to fed hypercarries, mainly due to the fact that the returned damage is calculated before resistances apply.

Wriggle's Lantern: Great lane-sustain item. Almost a must if jungling. Cheap item with great stats. Get this as ranged AD carry if you're far behind in lane, or if the ennemy team consists almost solely of AD champions. This item is a staple pick for many champions who want an early mix of offense, defense and farming capabilities.

Zhonya's Hourglass: A burst mage's wet dream. Burst in, and if you get focussed activate the hourglass. Expensive item, but well worth it if you're a typical burst mage, have to get close to your ennemies as mage, or have a point blank AoE spell or ultimate. Synergy with Annie, Fiddlesticks, Kennen, Morgana. The armor is merely a bonus, but it won't protect you much if the ennemies have fed AD carries. In this case, thornmail or wardens' mail are ppb better options.
When playing against an opponent using this item, switch focus if they activate it. Switch back again after the 2 seconds. Be careful not to overextend against ennemies wielding this item. If there are no other targets to switch to, use the 2 seconds to position yourself for the kill.

Abyssal Mask: Pretty straight-forward item. Get AP and magic resistance. The magic resistance it gives is rather high, so this is a great pick for AP carries. The aura makes it a superb item for supports such as Sona and possibly Janna and Taric.

Banshee's Veil: Used to be THE defensive item everybody should buy. It builds from a catalyst, which most champions benefit from anyway. The defensive stats are great (magic resistance + health), but the real reason this item is bought is the passifve effect. This item is GREAT against combo mages ( Brand, Annie, Sion, Veigar,...) or setups ( Blitzcrank, Ashe or Gragas initiations).
Don't get this item against sustained damage mages like Cassiopeia. Also, this item is very situational against Karthus, and it's effectiveness depends largely on the ennemy team and karthus' playstyle.

Athene's Unholy Grail In my opinion a very strong item, however you should NOT get this early as a defensive item. The reason for getting this should be the built-in blue buff rather than the magic resistance. Unless you're Galio, rushing this item delays your damage too much as a mage, pretty much making you useless throughout the early and midgame (which is when you should be at your strongest). If you get hardcountered in lane and need MR, I'd say Abyssal Mask is the better pick.

Force of Nature: Highest raw magic resistance in the game. Comes with increased movement speed and health regeneration that scales with health. This item was made for short-ranged champions. Great on initiators! Get this item if you're that high health frontliner ( Garen, tank(y) Cho'Gath, Singed, Udyr,...). Synergises well with Frozen Mallet, Warmog's Armor, Rod of Ages and Rylai's Crystal Scepter. Note that the synergy with rod and scepter are meh-ish, as casters generally shouldn't get this item.

Maw of Malmortius: This is a great item for AD champions who are in dire need of magic resistance. It's mainly meant for physical casters or champions who scale immensely with AD ( Riven, Pantheon, Talon,...). If your main damage comes from skills with AD ratio's, buy this over Wit's End. If you're more of an auto-attacker, get wit's.
Note: this item is also a decent counter to champions who want to quickly burst you down or have a way of sniping you off from a distance with magic damage. Karthus and Lux come to mind.

Mercury's Treads: The best boots in the game. If you're not getting these, you're either a ranged AD carry, an AP carry, or a crazy Tryndamere.

Quicksilver Sash: One of the strongest items in the game. Get this item if the opposing team has 2 or more of the following champions: Mordekaizer, Malzahar, Warwick, Urgot, Mordekaiser, Morgana, Skarner. The active effect overrides ANYTHING the ennemies throw at you. Of the above champions, it is especially harmful to Malzahar, removing Malefic Visions, breaking the surpress of Nether Grasp, AND removing the silence from Call of the Void.

Spirit Visage: Get this item if ALL the stats benefit you. Cooldown reduction and magic resistance benefit most champions, but increased healing doesn't. This does synergise with lifesteal and spellvamp.

Wit's End: If you're an auto-attacker, this item is a viable option. It gives you 2 types of damage (more physical damage from the increased attack speed, and on-hit magic damage), and gives substantial magic resistance. If as an AD champion you need to counterpick to magic damage but don't want to gimp your damage output too much, this item is generally better than Hexdrinker.

Some items are bought because they give overall defensive stat boosts, rather than selectively. I chose to create a different section for these.

Aegis of the Legion: A strong overall stat boost for your entire team. This item is definately worth it's gold. It's purchased by most support champions, as well as by Shen, as the stat increase intrinsically synergises with the way his ultimate is used.

Guardian Angel: A strong item, giving you a decent stat boost. This item synergises well with champions that are self-sustained (like Irelia with Hiten Style, who's also hard to cc down after the revive.), with champions with sick juking potential ( Akali, Katarina) and with other sources of revival ( Chronoshift and Rebirth for teh lulz.
Note that this item counters champions that require kills or assists to refresh cooldowns and snowball into fights like this. AP Master Yi, Katarina and Darius are examples. This item more or less hardcounters Katarina.

A short section on life steal and spell vamp.

These 2 defensive attributes are mainly anti-burst. They allow you to get bursted down to 2% hp, retreat a bit, heal up quickly, and be valuable again. In a 1v1 fight against a burst mage, if he doesn't kill you, you'll have the definate advantage if you have say a Bloodthirster, because the mage 'll have his cooldowns up, and you'll be healing up whilst hurting him bad.

In all, get life steal and spellvamp for small skirmishes and as an anti-burst tool that doesn't require you to sacrifice damage output.

I hope this guide was helpful to you.
You probabely haven't read it through entirely; it's not intended to be read through entirely. Yet if you reach this passage for some reason, I'd like to end stating that comments and improvements are always welcome!

PS:
I've been asked to give some information towards the ideal defensive setup. Now I know that somebody else has done the math on this, and I'm going to be lazy and just reference his guide: http://www.solomid.net/guides.php?g=11623