The Twin Blades of Azzinoth are a pair of weapons wielded by Illidan Stormrage. Azzinoth was a doom guard commander whom Illidan slew 10,000 years ago. Illidan took Azzinoth's twin warglaives and trained himself to use them. He has become exceedingly efficient with the weapons. When Illidan used the twin warglaives they were usually connected, but could be disconnected to form separate weapons. Once disconnected they could be reconnected to form a single weapon once more. The pit lordMagtheridon proved to be no match for the wielder of the Twin Blades of Azzinoth.
In Warcraft III, one of the warglaives' handgrips featured a small pandaren image (the symbol of Samwise Didier). This was used as an inside joke; the warglaives have no connection to Pandaria and their design has been modified for the Burning Crusade.
The Twin Blades of Azzinoth are the first legendary weapons that are a set. They are also the first legendary weapons of the Burning Crusade expansion that could be used outside an instance (The legendary weapons in the Kael'thas Sunstrider fight are limited to Tempest Keep). The two glaives were also the first permanent legendary items that did not require a quest to obtain.
In World of Warcraft, the blades cannot be combined into a single weapon. In the game, the Twin Blades of Azzinoth are a pair of legendary swords, a main hand and an off-hand, which can only be used by warriors, monks, Death knights and rogues. An early unobtainable version was presented as being able to function like described in lore.
Illidan splits his weapon into the Twin Blades of Azzinoth in Arthas: Rise of the Lich King. However, the combined weapon is never described, and the two resulting weapons are each called "a single blade". This may be an error, as it seems that he split only one of the warglaives into two even smaller blades.