Dragonglass is a common name in Westeros for the substance known as obsidian, a form of volcanic glass. It is one of the two known substances capable of killing White Walkers. It is also capable of killing wights. In Old Valyria, it was known as zirtys perzys, which translates to "frozen fire". Large amounts of dragonglass can be found on Dragonstone.

Dragonglass was a very important tool to the Children of the Forest, using it to fashion weapons. A long-forgotten secret is that the Children actually created the White Walkers as a weapon, by transforming humans into them: this was achieved in a magic ceremony that involved (among other things) plunging a dragonglass shard into a human's chest.