Kelly Bailey composed numerous short pieces of original incidental music that are interspersed throughout Half-Life 2. Several tracks from the Half-Life soundtrack were re-titled and carried over, while some were remixed.
The limited-edition Half-Life 2 "Gold" package included, among other exclusive extras, a CD soundtrack. Although the CD contained several exclusive tracks, it did not include all of the music used in the game.
In-game, energetic techno tracks tend to back significant battles, atmospheric synthesizer pieces enhance key plot and exploration moments and reinforce feelings of adventure, isolation, or melancholy in the player.
|1||Hazardous Environments||"A Red Letter Day": when Gordon puts on the H.E.V. Suit.|
|2||CP Violation||Route Kanal: as Gordon avoids being hit by the Razor Trains.|
|3||The Innsbruck Experiment||Route Kanal: when first fighting Metrocops wielding MP7.|
|4||Brane Scan||Anticitizen One: during the fight in the generator plaza.|
|5||Dark Energy|| Highway 17: when Gordon leaves Shorepoint Base in the Scout Car.
Dark Energy: during the first half of the credits.
|6||Requiem for Ravenholm||"We Don't Go To Ravenholm...": when Father Grigori bids farewell.|
|7||Pulse Phase|| "Follow Freeman!": during the Strider battle outside the Nexus.
Dark Energy: when Gordon descends in the elevator to face Breen.
|8||Ravenholm Reprise||"We Don't Go To Ravenholm...": when Gordon enters Ravenholm.|
|9||Probably Not A Problem||Route Kanal: during the Headcrab Shelling to Station 6.|
|10||Calabi-Yau Model|| Sandtraps: when Gordon enters the Vortigaunt Camp.
"Follow Freeman!": in the building surrounded by Overwatch Snipers.
|11||Slow Light||Highway 17: after Gordon defeats the Gunship at New Little Odessa.|
|12||Apprehension and Evasion|| "A Red Letter Day": after Gordon uses the Crowbar for the first time.
Sandtraps: during Gordon's raid to the bunkers on The Coast.
|13||Hunter Down||"Follow Freeman!": after Gordon kills the last Strider before proceeding to the horse.|
|14||Our Resurrected Teleport||"A Red Letter Day": when Gordon enters the Teleporter room in Kleiner's lab.|
|15||Miscount Detected||Exclusive to the Soundtrack release.|
|16||Headhumper||Exclusive to the Soundtrack release.|
|17||Triage At Dawn||"We Don't Go To Ravenholm...": when the battle in the garage is over.|
|18||Combine Harvester||Exclusive to the Soundtrack release.|
|19||Lab Practicum||Highway 17: when Gordon passes under the bridge.|
|20||Nova Prospekt||Nova Prospekt: as Gordon enters the cell blocks.|
|21||Broken Symmetry||Route Kanal: after Gordon leaves the sewers.|
|22||LG Orbifold||"Follow Freeman!": after Gordon is instructed to go to the horse.|
|23||Kaon||"Follow Freeman!": when Gordon fights the Combine Gunship on the Overwatch Nexus.|
|24||You're Not Supposed to Be Here||Water Hazard: after receiving the mounted gun for the Airboat.|
|25||Suppression Field||Anticitizen One: as Gordon finds his first Squad in the playground.|
|26||Hard Fought||Anticitizen One: during fights with Civil Protection, while assaulting a barricade and the underground shoot-out while waiting for a hole to be blown open by a rebel.|
|27||Particle Ghost||"We Don't Go To Ravenholm...": after Gordon leaves the Ravenholm Mines.|
|28||Shadows Fore and Aft||Point Insertion: during the G-Man's speech.|
|29||Neutrino Trap||Our Benefactors: as Gordon exits the sewer tunnel at the base of the Citadel.|
|30||Zero Point Energy Field||Route Kanal: when Gordon enters the sewers after the Hunter-Chopper attacks.|
|31||Echoes of a Resonance Cascade||Anticitizen One: upon entering the toxic underground tunnel.|
|32||Black Mesa Inbound||Black Mesa East: when Gordon and Alyx enter the scrapyard at Black Mesa East.|
|33||Xen Relay||Dark Energy: upon Gordon's arrival to Breen's office.|
|34||Tracking Device||Dark Energy: during the the second half of the credits.|
|35||Singularity||Entanglement: upon Gordon's arrival to the Nova Prospekt teleporter.|
|36||Dirac Shore||Entanglement: when Gordon enters the Depot's flooded basement.|
|37||Escape Array||Black Mesa East: as Gordon nears the dam's Electrical Station.|
|38||Negative Pressure||Our Benefactors: as Gordon leaves the combine elevator.|
|39||Tau-9||Highway 17: when Gordon enters the crane to move the Scout Car.|
|40||Something Secret Steers Us||Sandtraps: during the Dropship attacks at Lighthouse Point.|
|41||Triple Entanglement||Anticitizen One: when Gordon enters the sewers after Alyx is captured.|
|42||Biozeminade Fragment||Exclusive to the Soundtrack release.|
|43||Lambda Core||Water Hazard: as Gordon flees from the second Hunter-Chopper.|
|44||Entanglement|| Nova Prospekt: Upon entering the Combine Wall crushing canyon at end of chapter, just before meeting Alyx.
Route Kanal: At the beginning of the chapter, when the player is on the stairs waiting for the train to jump, if the player quick saves and then loads, this track will play.
|45||Highway 17||Sandtraps: In a house just outside the zombie-infested tunnel, where a few Rollermines also break in an attempt to attack Gordon.|
|46||A Red Letter Day||A Red Letter Day: upon entering Kleiner's lab for the first time.|
|47||Sand Traps||Sandtraps: When driving through the tunnel full of zombies.|
|48||CP Violation (Remix)||Route Kanal: Upon leaving the pool with a mixer in it, where Civil Protection proceed to roll explosive barrels at the player.|
|49||Train Station 1||Point Insertion: This music plays just outside the City 17 Trainstation, when seeing City 17 for the first time.|
|50||Train Station 2|| Point Insertion: Plays when being chased in the rooftops.
Follow Freeman: Plays when seeing a dropship from the Overwatch Nexus.
|51||Radio||Anticitizen One: Plays while the TV with G-Man on it is turned on.|
- Bailey's affinity for wordplay is evident in his track titles, as they often reference real world subjects as well as in-game facts:
- Triage at Dawn references the same situation the player finds himself at the point it is played; Triage of Winston at dawn break.
- LG Orbifold is a theoretical physics geometry term mentioned by Dr. Kleiner while checking teleporter parameters moments before teleporting Alyx.
- Zero Point Energy Field is a reference to the Zero Point Energy Field Manipulator.
- Xen Relay is a reference to Dr. Mossman's speech about how they control a Xen Relay.
- Tracking Device is a reference to the fact that the HECU and the Combine have been using the tracking device in Freeman's HEV suit to easily track and ambush him.
- Something Secret Steers Us is taken from the Vortigaunts quote "Something secret steers us both. We shall not name it."
- Tau-9 is a reference to the Tau Cannon present in the Scout Car.
- CP Violation is a violation of charge conjugation parity symmetry) in particle physics.
- Many of the songs on the Soundtrack are either remixes or simple name changes of songs from the Half-Life Soundtrack:
- Hazardous Environments is a renaming of Valve Theme (Extended).
- Zero Point Energy Field is a renaming of Cavern Ambience.
- Lambda Core is a remix of Diabolical Adrenaline Guitar.
- Black Mesa Inbound is a renaming of Vague Voices.
- Singularity is a renaming of Traveling Through Limbo.
- Echoes of a Resonance Cascade is a renaming of Space Ocean.
- Tracking Device is a remix of Credits / Closing Theme.
- Biozeminade Fragment is a remix of Alien Shock.
- Something Secret Steers Us is a renaming of Nuclear Mission Jam.
- Pulse Phase is actually a truncated version of Dark Energy, slowed down by 50%.
- Tau-9 is a renaming of Drums and Riffs.
- Radio is composed of two samples that come from the 1995 sample library Cuckooland: Ghost in the Machine from Zero-G, composed by Ian Sanderson and Simon Mills. The first one is called Distorted Trumpets, while the second one, whose pitch has been raised, is called Is that the Door?
- Half-Life 2 Soundtrack on YouTube
- Half-Life 2 Soundtrack on Spotify
- Half-Life 2 Soundtrack on Apple Music