"Through the Looking Glass" is the twenty-second episode and season finale of the third season—sixty-ninth episode overall—of the ABC television series Lost. It was written by co-creator/executive producer Damon Lindelof and executive producer Carlton Cuse, and directed by executive producer Jack Bender. ABC Medianet, (May 7, 2007) "12" target="_blank">Lost Season Finale Entertaiment Press Release". Retrieved on July 3, 2007. When first aired on May 23, 2007 in the _United States and Canada, it was watched by an average of fourteen million American viewers. ABC Medianet, (May 30, 2007) "06" target="_blank">Weekly Entertainment Primetime Ratings Wrap-Up Report Press Release". Retrieved on July 3, 2007. Like the previous two season finales, it was two hours long with advertisements, twice the length of a normal episode. It was edited into two individual episodes when released on DVD. The season finale was critically acclaimed and the episode has garnered a number of awards and nominations, including three _Emmy nominations and a DGA Award nomination. Academy of Television Arts & Sciences, (July 19, 2007) "db" target="_blank">Primetime Emmys Complete 2007 Nominations List". Retrieved on August 5, 2007.

The episode begins its narrative in late December 2004, over ninety days after the crash of _Oceanic Airlines Flight 815. The battle between the crash survivors and the dangerous and mysterious island inhabitants referred to as the "Others" comes to a head as ten of the Others attack and are then ambushed at the survivors' camp and are subsequently killed. Meanwhile, Jack Shephard (played by Matthew Fox) leads most of the survivors to the island's radio tower to communicate with a nearby ship. Intercut with this story are off-island scenes spotlighting Jack, who has become near-suicidally depressed and addicted to painkillers. In a twist ending, it is revealed that these scenes are flashforwards to sometime in the future, after Jack has left the island, rather than flashbacks as in previous episodes of Lost.