Skyrim:Skills

Skills400px|thumb|The skills menu
There are 18 skills in Skyrim, each of which determines how well various tasks can be performed. As skills are used, they increase in level, which increases the character's overall level. The starting value for most skills is 15, although each race confers bonuses to certain skills. Skills can also be increased by reading skill books, learning from trainers, or as a reward for completing certain quests.

Guards will often comment on your skills when you are near them.


 

Perks
Perks are a new feature in Skyrim. Each skill has its own associated perks, which can be unlocked when a character advances a level. 180 skill perks are available, 251 if including all ranks for each perk. The perks are all detailed on the individual skill pages, along with their requirements. One perk point is given to the character when the character's overall level increases. The maximum value for unused perk points is 255, four more than required for every perk. Leveling up with 255 unused perk points will cause the counter to roll back to zero and restart.

Most perks have both a skill level requirement and a prerequisite perk that must first be unlocked to make the perk available.
When a prerequisite perk has more than one rank, only the first rank needs to be unlocked to make the next perk available. For example, to unlock Enchanting's "Fire Enchanter" skill, only the first rank of "Enchanter" needs to be unlocked, not all five ranks.
When a skill has two prerequisite perks, only one of the two perks needs to be unlocked to make the next perk available. For example, to unlock the "Extra Effect" skill under Enchanting, only "Storm Enchanter" or "Corpus Enchanter" needs to be unlocked.
Perk points cannot be changed or undone once spent. 
With Dragonborn installed, perks may be undone and redistributed at the cost of one dragon soul per skill tree once you have completed the add-on's main quest. See this page for details.
The Official Skyrim Patch version 1.9 allows a skill at level 100 to be made Legendary, which will reset the skill to level 15 and refund all perk points allocated to that skill, making them available for reallocation wherever you see fit.
Players cannot 'loop round' later perks to unlock earlier ones. An example of this would be the Smithing skill tree; on the left-hand side of the circle are light armor perks, on the right are heavy armor perks, meeting in the middle at dragon armor at level 100. Although the dragon armor perk is visibly joined to both the glass armor and daedric armor perks, it is not possible to unlock all 3 without first acquiring all the prerequisite light and heavy armor perks.
Prior to Patch 1.9, it is only possible for a character to unlock 80 of the 251 skill perks; PC users can use the console command   to unlock any desired perk.

Skill Advancement
The skill advancement mechanism differs between skills. For example, by selling higher value items to merchants, the player gains experience in their Speech skill. Smithing skill increases have been altered by Patch 1.5, they now increase more depending on value of forged equipment. When using a grindwheel or table, the amount by which the enhanced equipment value goes up defines how much experience is gained for it. With 90 smithing and 100% smithing enchanted gear, enhancing an ebony bow from base quality increases experience almost by an entire level. For more details, see each skill's article.

Trainers can help level up a skill for a maximum of five times per character level. Unused training sessions do not carry over to the next level.

For information on how to gain free skill boosts, see this page.

Legendary Skills
400px|thumb|The skills menu showing Legendary Skills and broken level cap
Version 1.9 of the Official Skyrim patch allows skills to be reset to their minimum of level 15 and subsequently retrained to gain further experience, while refunding any perk points allocated to that skill. Being able to gain extra experience this way, by leveling a skill from 15 to 100 twice (or more) instead of once, allows the player to exceed the previous level cap of 81, and eventually gain enough skill perks to have all the perks for all skills, at the cost of their current proficiency in the skill every time it is made "legendary". Each skill can be reset multiple times, and they will be marked with the symbol of the Imperial Dragon and a number indicating how many times it has been reset if done so multiple times. In order to unlock all skill perks, the player needs to reach level 252. For a level 81 player with all skills at 100, this requires skills be reset 147 times (or, on average, 8 or 9 resets of EACH skill - although it is better to reset some skills more often than others, and others only a few times or even not at all), with each skill that was reset brought back to level 100.

Note, however, that if the player ever reaches more than 255 unspent perk points, the number of perk points available rolls over to zero at 256 unspent points and starts over, causing you to lose those points.

Some things need to be borne in mind when making a skill Legendary.

Gaining extra levels - from regaining skills - can, up to a point, result in monsters that scale to your level getting tougher, while you're temporarily weaker on account of having given up a skill. Make sure you still have the ability to defeat tough foes even if it's a weapon or Armor skill that you reset (e.g. have a powerful follower, or don't reset all your weapon skills at once.)
You don't, of course, regain the ability to gain skill points from a book to boost the skill, or any of the other one-off rewards that you used on the way up. So you're going to have to re-level most skills the hard way.
If you have learned a spell, you keep that spell, and can thus cast high-level spells at low-level skill, to level up quickly - as long as you have the magicka for it. This applies to Destruction, Conjuration, Restoration, Illusion, Alteration. And of course if you have enchanted gear that reduces spell costs, this still works.  Note that Destruction spells require a target, Conjuration spells require the presence of a foe, Alteration requires a thing to be altered, Illusion can require people to trick (including civilians and non-combatants), and Restoration healing spells need to actually heal damage which means that you or somebody nearby have to have been hurt.  Undead-turning spells require the presence of an undead - of course this may include you if you are a vampire.  Some of the spell skills which are the hardest to reach level 100 in the first place, are the easiest ones to Legendary over and over again if you are properly prepared.
Knowledge of alchemical properties and enchantments is of course retained. (This also means, no more gaining experience by re-learning an alchemical property, or disenchanting an item, but you already know the good recipes.) You're limited by how many ingredients you can get hold of, so stock up.
Although armor, block and smithing skills can be reduced to nothing, you obviously still keep the good quality armor you found or made earlier - and all the Health from the previous actual levels you've gained - so you can train up Armor and Block skills very quickly by equipping your best armor and going toe-to-toe with a giant, which of course wasn't possible when trying to level up armor the first time. Going toe-to-toe against a giant with low Armor skills is also a good opportunity to boost Restoration in the process.
Likewise, weapons and weapon skills (One-handed, Two-handed, Archery). Note that enchantment damage on weapons (+fire, +frost, +shock etc.) does not contribute towards the skill. It appears that increasing a weapon's damage by tempering it, or putting perk points in the weapon skill, does not actually cause the skill to increase any faster: indeed, by doubling the damage output without actually doubling the experience gained, you end up needing to find twice as many enemies if you want to level up against enemies, rather than by training against an essential/regenerating non-hostile target (e.g. Shadowmere, Hadvar, Ralof). So for the most efficient retraining, you want a weapon made of the highest quality material but not tempered or enchanted. "Bound" weapons (classing as Daedric) qualify for this, as do actual daedric, ebony or dragonbone. 
Losing all the Smithing perks means that you can't improve future weapons to the same degree as before, until you regain the skill level and perks. (And all those iron building materials that you made for the "Hearthfire" homes don't need to be made a second time.) Jewelry, of course, is unaffected by this, since it requires no perks: and you are free to stock up as many ore ingots as you wish to use in regaining skill levels. Stocking up on high quality Fortify Smithing potions helps give more skill xp from tempering, but not from initially forging a weapon or making jewelry.
Lockpicking has the awkward feature that if you have already picked a given lock, but it has since reset to locked (e.g. a house overnight, or a door or chest in a dungeon that has respawned after clearing), you do not get experience for picking that lock a second time. So it is possible, and eventually inevitable, to actually run out of locks to pick that will actually improve your skill. Even the training locks in the Thieves Guild are subject to this: and once this hits, you eventually get to a place where Lockpicking can only be boosted by paying gold for training (limited to 5x per level) or breaking lockpicks while failing to pick a lock. Failing to pick a lock with the Skeleton Key gives no experience, since the Skeleton Key does not break... Thus, Lockpicking is probably better to keep at 100 and never make it legendary at all, or at least not more than once (there are enough locks in the game to level Lockpicking up to 100 at least twice, maybe three times if you really cast around and have all the expansions).
A lot of pickpocketable items do not respawn in the pockets of people around the kingdom: so you can likewise run low on pockets to pick when trying to level it a second time. There is, however, always the option of paying for training (in any skill, doesn't even have to be pickpocketing) and pickpocketing the gold back, or indeed of doing "fishing" (pickpocket) jobs for Delvin Mallory in the Thieves Guild, since this creates items in the target's pockets to be picked. The latter is reliable but can be a bit slow because of all the travelling involved. Leveling Pickpocket up to 100 a second time should be entirely possible.
A merchant who has been invested in with the "Investor" perk, does not lose that investment when you lose the perk - they retain the higher amount of gold even when you no longer have the perk. Conversely, you cannot invest with them a second time after re-leveling Speech to a high enough level to re-gain the perk. However, losing the Merchant and Fence perks removes the ability to sell any item, or stolen items, to any merchant: so you will have to re-allocate points to these perks when your Speech gets back to the appropriate level.
All the various Speech challenges (persuade / intimidate / bribe) can usually only be done once - the few exceptions (other than bribing / persuading respawning guards to ignore a crime) are glitches, mostly fixed by the Unofficial Patch - so if you decide to make Speech legendary, chances are that your only way of regaining the experience is buying and selling items, and that's going to be a LOT of gold value of items bought and sold.  High level Alchemy and Smithing are essential for producing such items to sell, as is setting up all the Thieves Guild fences in advance since they have a much higher gold max. 
Especially if you haven't exploited the synergy of Fortify Alchemy / Enchant / Restoration to make gear with stats and value in the millions.  Of course if you *have* exploited that glitch, it's possible to have glitched Fortify Enchant + Smithing potions and Fortify Alchemy + Smithing equipment to be able to boost Alchemy and Smithing from 15 to 100 in one go, then sell an item created that way to boost Speech from 15 to 100 in one go. Though this has been fixed by the Unofficial Skyrim Patch, in both Legendary and Special Editions. Without this exploit, it may be a better policy *not* to make Speech legendary - especially considering the loss (albeit temporary) of the Merchant and Fence perks: if you want to do it, do it just once.
Since Enchanting skill gains are based only on the number of items enchanted, or soul gems used to recharge depleted items, leveling Enchanting is no different the second time to the first. Even potions of Fortify Enchant don't affect the skill gains. Stocking up on filled soul gems and items to enchant, is what you need.
Sneak is likewise pretty much exactly the same to level up a second or subsequent time, as it was the first time round. It's just easier to do once you know where to find the right kind of situation to train sneaking.
Several perks are applied permanently, even if the related skill is reset and the perk points are returned. These are: Golden Touch, Investor, Master of the Mind, Master Trader, Persuasion, Ranger, Treasure Hunter, and Quick Reflexes  . Consider spending perks points to unlock these before resetting your skill.

Achievements
Achievements related to skills are:






Notes
When pending a character level increase, leveling up skills will add to the progress bar of the next level.
In the skills menu, the nebulae in the backgrounds of the three different categories of skills have the shape of the correspondent category: a mage for the magic skills, a thief for the stealth skills, and a warrior for the combat skills.
Some quests are only offered to characters who have certain sufficiently developed skills, specifically, the quests given by mages of the College of Winterhold when you have reached a skill level of 90 or 100 in one of the six schools of magic.
Increasing developed skills leads to faster character level increases.
Faster skill increases are possible by activating certain Standing Stones.
Even though Archery is considered a Combat Skill, Thief Stone enhances the skill gain in Archery, not Warrior Stone.
If you are using a potion or spell that modifies one or more of the skills, making those skills Legendary will cause those modified skills to not level up again. To fix this, be sure that the spell effect has expired, so that the skill being reset will default back to their normal start level. To be sure you have it set correctly, the skill level should appear in white, instead of the green or red used for modified levels.  
Because Skyrim does not have classes, the distinction between major and minor skills from previous Elder Scrolls games does not exist any more — characters do not have a predetermined list of skills that increase more quickly.
Skills from Oblivion that have been removed without a singularly-defined replacement include:
Armorer: Weapons and armor no longer require repair, though smithing allows the player to improve these items and create new weapons and armor.
Athletics and Acrobatics: Running, jumping, and swimming ability are now based entirely on race though you can sprint longer with more stamina.
Blade and Blunt: Weapon skills are instead divided into One-handed and Two-handed skills. Perks within those skills allow you to specialize in certain weapon types.
Hand to Hand: No true replacement, although various features enhance unarmed combat (Khajiit have claw attacks; a Heavy Armor perk increases hand-to-hand damage; an enchantment effect for increased hand-to-hand damage exists via the Gloves of the Pugilist)
Mercantile and Speechcraft: Combined into the Speech skill.
Mysticism: Spells shifted to other magic skills
Skills from Oblivion that have been renamed:
Marksman: Replaced with Archery
Security: Replaced with Lockpicking
Skills from pre-Oblivion games that have returned:
Morrowind's Enchant returns as Enchanting.
Daggerfall's Pickpocket returns as Pickpocket.