From StrategyWiki, the free strategy guide and walkthrough wiki

Mesmers use spells that either steal energy, add domination penalties, or add status effects to enemies.

[edit] Attributes

Fast Casting (primary)

Fast Casting allows Mesmers to use spells faster than any other profession.

Domination

Domination increases the amount or duration of spells that give domination penalties (e.g. take damage upon casting a spell)

Illusion

Illusion increases the amount or duration of spells that give status effects to enemies (e.g. hinder movement, or drain health)

Inspiration

Inspiration increases the amount that spells which steal energy from enemies are effective for.

[edit] Skills

For more details on skills, see Guild Wars/Mesmer/Skills.