Charm

Charm effects are a form of crowd control that gives control of a victim to the caster. This control can either be direct, giving the caster the same control as a Hunter pet (or his own character) or indirect, causing the victim to "switch sides" and physically attack his former allies with no additional actions needed from the caster. Some charm spells effectively put the caster to sleep while he controls his target.

The Undead racial ability [Will of the Forsaken] breaks charms and renders a player immune to it for 5 seconds as of the 1.6.0 patch. Charmed creatures will not neccessarily be freed by damage, but damaging and "waking" the caster usually will.

Any charm, no matter the duration listed, will last a maximum of 15 seconds when used against players in PvP.

Examples of abilities that Charm opponents:

• Priest: [Mind Control]
• Engineers: Gnomish Mind Control Cap, Gnomish Universal Remote (mechanical targets only)
• Warlock: Enslave Demon (demons only)
  • A Warlock's pet Succubus can use the [Seduction] skill which is technically a "Charm" effect and can be dispelled as such, but acts more like a regular Sleep effect.

Counters

• The PvP Trinkets
• Hunter pets of hunter's with the [Bestial Wrath] talent are immune to charm.
• Warrior's [Commanding Shout] may dispel charm.^{[citation needed]} 
• Forsaken characters can use their racial trait [Will of the Forsaken] to dispel charm.
• Some objects can apply a debuff that grants immunity to charm.
• Shaman's Tremor Totems remove charm effects.

Patch Changes

• Patch 1.4.0 (2005-04-19): "Charm and Polymorph mechanics can now be reactively countered by spells and abilities (e.g. Druid Shapeshifting will now cancel Polymorph effects)."
  
• Patch 2.1.0 (2007-05-22): "Insignia of the Alliance/Horde and Medallion of the Alliance/Horde now remove Fear, Stun and Polymorph effects and no longer remove Charm effects."