The Last of Us: Left Behind is an action-adventure game developed by Naughty Dog and published by Sony Computer Entertainment. It was released worldwide for the PlayStation 3 on February 14, 2014, as a downloadable expansion pack to The Last of Us; it was later bundled with The Last of Us Remastered, an updated version of the game released for the PlayStation 4 on July 29, 2014, and was released as a standalone expansion pack for both consoles on May 12, 2015.

Set in a post-apocalyptic world, players control Ellie, a teenage girl who spends time with her best friend Riley after Riley's unexpected return. The Last of Us: Left Behind is played from a third-person perspective; players use firearms, improvised weapons and stealth to defend against hostile humans and zombie-like creatures infected by a mutated strain of the Cordyceps fungus.

Players can use "Listen Mode" to locate enemies through a heightened sense of hearing and spatial awareness. The game also features a crafting system, allowing players to customize weapons through the upgrades. The Last of Us: Left Behind was highly anticipated due to the critical success of The Last of Us. It was positively-received by reviewers, with particular praise for its story, characterization, and depiction of female and LGBT characters. It has won several awards and accolades from multiple gaming publications since its release.

In the aftermath of a fight that leaves Joel (Troy Baker) severely injured, Ellie (Ashley Johnson) searches an abandoned mall for supplies to heal him. She discovers a medical kit in a derelict military helicopter. Making her way back to Joel, Ellie is impeded by the Infected and members of a hostile human group. She fights her way back to the unconscious Joel, treats his open wound, and takes him to find a hideout for the coming winter.

Months earlier, before Ellie meets Joel, Ellie's friend Riley (Yaani King) surprises Ellie at their boarding school after weeks away. She reveals that she has joined the Fireflies, a revolutionary militia group, and takes Ellie to explore an abandoned shopping mall. Riley reveals that she has been assigned to a group of Fireflies in a different city, and broke the rules to see Ellie again. The girls argue, but Ellie eventually tells her that she supports her decision as it is something that Riley has wanted for a long time.

Before parting, Riley plugs Ellie's walkman into the sound system and dances with her. Ellie tearfully begs Riley not to leave. Riley rips her dog tags off and Ellie kisses her. Drawn by the noise, the Infected pursue Ellie and Riley; they run, but are bitten. They consider suicide, but choose to spend their final hours together.