City of Glass is the third book in The Mortal Instruments series, an urban fantasy series set in New York written by Cassandra Clare. It was originally published in the United States in hardcover on March 24, 2009.
Picking up from City of Ashes, City of Glass begins a few days after Clary and Simon's awkward break-up. With the permission of the Clave and Alicante, Magnus Bane creates a portal to send the Lightwoods, Jace, Clary and Madeleine to Alicante. Desperate to keep Clary safe, Jace lures Simon to the Institute and asks him to lie to the Lightwoods about Clary not wanting to go to Idris. Simon refuses, but their argument over the issue is interrupted when the Institute is attacked by Forsaken. During the attack Madeleine is killed. Simon is seriously injured, which leaves Jace with no choice but to bring him through the portal as well or risk the Forsaken killing him.