Half-Life 2: Episode One is the first in a series of episodes

Episodic games

An episodic video game is a video game of a shorter length that is commercially released as an installment to a continuous and larger series. Episodic games differ from conventional video games in that they often contain less content but are developed on a more frequent basis.Such a series may or...

 that serve as the sequel for the 2004 first-person shooter

First-person shooter

First-person shooter is a video game genre that centers the gameplay on gun and projectile weapon-based combat through first-person perspective; i.e., the player experiences the action through the eyes of a protagonist. Generally speaking, the first-person shooter shares common traits with other...

 video game Half-Life 2

Half-Life 2

Half-Life 2 , the sequel to Half-Life, is a first-person shooter video game and a signature title in the Half-Life series. It is singleplayer, story-driven, science fiction, and linear...

. It was developed by Valve Corporation

Valve Corporation

Valve Corporation is an American video game development and digital distribution company based in Bellevue, Washington, United States...

 and released on June 1, 2006. Originally called Half-Life 2: Aftermath, the game was later renamed to Episode One after Valve became confident in using an episodic structure for the game. Similar to Half-Life 2, Episode One also uses the Source game engine.