Oblivion:Illusion

Use the school of illusion to create light, conceal, charm, paralyze or alter an actor's aggression or confidence.

In-game Description: Cast spells to charm, conceal, create light, silence, paralyze, command or affect morale or aggressiveness.

Mastery
Mastery Perks
A Novice can only cast Novice level Illusion spells.
An Apprentice can cast up to Apprentice level Illusion spells.
A Journeyman can cast up to Journeyman level Illusion spells.
An Expert can cast up to Expert level Illusion spells.
A Master can cast all Illusion spells.

Skill Benefits
As your illusion skill increases, the Magicka cost to cast illusion spells decreases, according to the following equation:
 Cost = BaseCost * (1.4 - (0.012 * Skill))
The maximum value for Skill in this equation is 100; increases past 100 will not continue to decrease spell-casting cost.

Skill Increases
You gain 3 experience points every time an illusion spell is cast upon an appropriate target, regardless of the magicka cost.

General tips for increasing spell-casting skills are provided at General Magic Strategies.

Many of the novice illusion spells are good for practice.  Starlight is the only novice spell that can be cast upon yourself.  Many of the other novice spells are cheaper, and can be cast on any townsperson without any negative consequences; Inspiration and Inspiring Touch are the cheapest spells.

To create a custom practice spell, the cheapest illusion effect that can be cast upon yourself is Light.  Rally is an even cheaper effect, but it is not possible to create a cast-on-self Rally spell (but as above, this effect can safely be cast on townspeople). 

See also:
Increasing Skills: General tips on how to improve your skills semi-naturally.
Trainers: Pay for illusion lessons.
 
Skill Books: Books that provide lessons in illusion.
Increasing Attributes: Tips on training skills to improve the Personality attribute.
Free Skill Boosts: Vampires gain a free illusion skill boost.
Magic Items: There are multiple generic items with the fortify illusion enchantment.
Unique Items: A list of unique items, some of which fortify the illusion skill. These do not include Leveled Items such as those received from quests, or Artifacts.
:Unique items include:
::*Shrouded Armor, which is awarded upon joining the Dark Brotherhood after the quest A Knife in the Dark. Among other enchantments, the armor fortifies the illusion skill by 8, while the hood fortifies the illusion skill by 2.
::*Black Hand Armor is a unique set consisting of a robe and a hood. Among other things the robe fortifies your illusion skill by 11 points, while the Black Hand Hood fortifies your illusion skill by 4 points.

Dialogue
When your skill reaches 70 or higher, NPCs will start saying: "You have the hands of an illusionist".

Character Creation
The following races provide initial skill bonuses in illusion:
+5 bonus: Altmer, Argonian, Breton

The following standard classes include illusion as a major skill:
Agent, Bard, Healer, Knight, Mage, Rogue, Spellsword

If you choose Illusion as one of your major skills, you will start with two Illusion spells: Soothing Touch and Starlight. 

Magical Effects
A list of all standard illusion spells can be found on the Spells page.  The following individual effects are all considered to be part of the school of Illusion (see the individual effect pages for full details on availability; the Magical Effects article also provides a summary):



Messages
The following table provides the messages that are displayed when your Illusion skill levels up.



Notes
The most powerful (but also most costly) of all the Illusion spells in combat is Paralyze.  Even the toughest opponents can become easy targets when paralyzed.  Act quickly: paralysis does not last long unless you have a very high-powered spell. Some of the more powerful enemies such as Mankar Camoran and Mehrunes Dagon are immune to paralysis.
With demoralize (enemies run), frenzy (enemies attack each other), command, invisibility, silence, and paralyze, Illusion magic has more ways to protect you from combat and injury than any other school of magic. It is excellent as a primary stealth skill, and its abilities lend themselves extremely well to high difficulty games, where you can't afford to take damage.
The Bravil Mages Guild specializes in illusion; Delphine Jend and Ita Rienus sell the most illusion spells.
If you visit the Apprentice birthsign doomstone you can receive the greater power Void Seed.  This power fortifies your illusion skill 20 points once a day for 120 seconds.
Once your combined Fame and Infamy reaches 40, you can visit the Sithian heaven doomstone to receive the greater power Sithian Web.  One of several benefits of this power is that it fortifies your illusion skill 20 points once a day for 120 seconds.