Unlocks upon completion the 1st story mission: New Beginning.

Unlocks upon completion the 2nd story mission: Waste Disposal.

Unlocks upon completion the 3rd story mission: Pest Control.

Unlocks upon completion the 4th story mission: Crack in Defence.

Unlocks upon completion the 5th story mission: Black Coast.

Unlocks upon completion the 6th story mission: Final Push.

Unlocks upon completion the 7th story mission: The Beacon. This achievement unlocks shortly after The Purpose, subsequent to the postgame cutscene featuring the G-Man.

Unlocks upon acquiring Gordon's iconic, ever-trusty crowbar, which is embedded in the wall of the spawnroom of Chapter 1: New Beginning. Simply move within close range of the implement, and it will automatically be added to your inventory. The Crowbar is of utility in conserving ammunition when breaking supply crates, padlocks, and suchlike.

Unlocks upon deactivating the first Combine Barricade of the campaign. Shortly after beginning Chapter 1: New Beginnning, the player will ascend a flight of stairs, at the top of which is a Combine Interface connected to a power outlet. The player is required to remove the corresponding plug from the socket, thereby deactivating the Barricade.

Unlocks upon neutralising the Combine Gunship encountered towards the end of Chapter 3: Pest Control. On 'Normal' difficulty, it takes 7 hits from the Resistance RPG to down. Before engaging the Gunship, it is advisable for players to take stock of the Health and HEV Suit Chargers on the left side of the central column—these can be utilised as may be necessary throughout the entirety of the boss fight, which is single-stage. Whilst engaging the player, the Gunship routinely strafes to either side, such that it can attain direct line of sight; to negate this, the player should circumambulate the central column accordingly. Both prior and subsequent to engaging the player with its Pulse Cannon, the Gunship issues an audible mechanical groan.

Unlocks upon completion of the battle sequence towards the end of Chapter 6: Final Push. This set piece involves a multitude of Combine Soldiers and Combine Elites, in addition to several Striders. Once all Combine forces are neutralised, entering the communications tower to the left of the bridge will award the achievement.

Unlocks upon destroying the eponymous beacon, during Chapter 7: The Beacon.

Unlocks upon the first sighting of the G-Man. This encounter occurs during Chapter 2: Waste Disposal, subsequent to a brief firefight wherein Combine Soldiers emerge from behind a garage door to engage a group of Zombies. After combusting an explosive barrel to breach the compromised concrete wall opposite the aforementioned door, proceed to the sewers. Head towards the end of the chamber to find an iron grate on the left, a portion of which is missing. Utilise a nearby barrel to access the opening, and proceed to the end of the passageway, affording due caution to the Barnacle attached to the ceiling of the right side. At the end lies an iron grate wherethrough the G-Man can be observed strolling along the beach.

Unlocks upon occasioning a Zombie to self-immolate. Unforseen #1 and Burn! may be obtained in quick succession. After navigating a particularly confined and claustrophobic network of unilluminated tunnels (notably including the first Poison Zombie of the campaign), the player is required to negotiate a series of copper pipes in order to reach the area's upper level. Having done so, the player will find themself on a perforated steel walkway, with white paint railings on either side. Saliently, one of the two large copper pipes now to the player's right has ruptured, resulting in a leakage of flammable gas debarring the player from progressing. By exercising a modicum of trigger discipline, the player is able to encourage the approaching Zombie to walk directly into said gas, resulting in its unceremonious cremation.

Unlocks upon the second sighting of the G-Man. This encounter occurs during Chapter 3: Pest Control, subsequent to exiting the facility for the first time. Make your way past the Antlion Soldiers to the Resistance compound. The player will be beckoned inside; instead, take the path to the right, which leads up the mountainside. Once at the top, approach the railings to the left, and look towards the Combine ATV parked on the overlook to catch a second glimpse of the G-Man, this time entering a tunnel.

Unlocks upon restoring power to the Combine Interface. During Chapter 3: Pest Control, the player will be required to activate a generator, granting access to an upstairs office containing an inactive Combine Interface. Affixed to the switchboard opposite is a 'Remember' note, to aid the player with operation.

Unlocks upon disabling the Resistance analogue radio at the beginning of Chapter 4: Crack in Defence. The radio reposes on the second wooden desk in the left corridor, beside the Colt Python (.357 Magnum Revolver). Simply use any weapon in your arsenal (including the Crowbar and the Zero Point Energy Field Manipulator) to damage the radio to the extent whereat it no longer emits any sound.

Unlocks upon sighting the ghostly apparition in the lantern room of the lighthouse, during Chapter 5: Black Coast. As is the case for Unforseen #1 and Unforseen #2, this achievement is time-sensitive, and it is therefore advisable for the player to look towards said lantern room immediately after disembarking the vehicle.

Unlocks upon 'going down' the slide in the playground to the left of the lighthouse, during Chapter 5: Black Coast. There is no custom animation for 'going down' the slide, nor is the main portion of the slide accessible from the top of the adjoined ladder. The achievement is awarded for simply making contact with any part of the main portion of the equipment.

Unlocks upon flushing the lavatory on the first floor of the abandoned house, during Chapter 5: Black Coast. The door immediately before the lavatory has no particular unlock condition, so simply open it, enter the room, and interact with the lavatory.

Unlocked upon gaining access to the armoury in the abandoned house, during Chapter 5: Black Coast. Said armoury is located at the back of the room housing the four car battery bays that provide power to the electronic gate beside the house. Unlocking the door to the armoury requires a key, which can be obtained by using a car battery in the bay of the outhouse, to restore power to an electronic gate mechanism.

Unlocks upon shooting the Garden Gnome (Gnome Chompski) into the core of the beacon, during Chapter 7: The Beacon. After activating the override sequence and waiting for the windowpane to shatter, the player should use the Zero Point Energy Field Manipulator (Gravity Gun) to project the Garden Gnome. It is highly advisable for the player to create a save file shortly before doing so, in case the player misses the shot—ensure to account for a bit of bullet (or gnome, as the case may be) drop. Fortunately, no knowledge of the Coriolis & Eötvös Effects or external ballistics should be required for one to make the shot first time.