Counterspell

Counterspell is a mage spell that interrupts enemy spellcasting. When successful, the caster may not use the interrupted spell school for 7 seconds. For example, counterspelling a priest's Greater Heal will not only interrupt the heal in progress, but also prevent him from casting Holy spells for 7 seconds.

It is learned at level 9 for.

Talent improvement
The Improved Counterspell talent will also silence the enemy for 4 seconds.

Tips and tactics
This is a very potent spell in the mage arsenal when fighting enemy casters. Mages should learn when to use it.

In PvE groups, use counterspell to pull ranged casters into the group. Chasing down a creep that is casting from range can be risky if other creeps are in aggro range. Counterspell will cause it to run towards your group, where it can be more safely killed. The spell generates a high amount of threat, so a mage casting it may find themselves at the top of the mob's hate list.

Counterspell is a "twitch" spell, requiring good reaction time. Consider placing this spell on an easily accessible hotkey. One possibility is to use extra mouse buttons, such as the middle scroll wheel or thumb buttons if your mouse has them.

The Blizzard UI will show your target's cast bar. On the Interface Options page, select the "Show Enemy Cast Bar" options to display the bar. The cast bar appears below the target unit frame when the target is casting. Also, some addons will allow you to move and resize the enemy cast bar to make it more visible.

Shields that absorb damage such as Priest Power Word: Shield and the Paladin Blessing of Protection do not stop Counterspell. However, Invulnerability effects such as Paladin Divine Protection make your target immune to everything except Priest Mass Dispel, and your Counterspell will be wasted.

If improved by the talent Improved Counterspell, the 4 second silence will take effect whether you actually counter a spell or not (the counter effect still only works when you interrupt a spell). The silence effect is dispellable. You can use this "quirk" to interrupt a spell before it is even cast, should that be a good tactic to use at that moment. For example, you're fighting a priest or priest-like creep with an instant heal. They are almost dead, but have yet to cast their save-me spell. You can counterspell before they cast, giving you a four second window to kill them before they can recover and heal. Improved Counterspell is a good way to stop instant spells which have no cast time, and thus cannot be interrupted. Besides, Priest Silence is also a good way.

While Counterspell is almost useless against warriors and rogues, it can be used to bring them into combat preventing them from using Charge or Stealth. It has a range of 30 yards. Given most other instant spells have cooldowns, if the mage intend to use polymorph which heals the opponent, casting Counterspell to start combat does not waste any cooldown.

This spell can also be used to bring a mob group together in order to cast AoE spells on them.

Helpful macros
This macro will make your Counterspell hotkey more responsive, by stopping any current spell casts in progress. Since Counterspell is not affected by the global cooldown, the macro will work at any time.

/stopcasting /cast Counterspell