Play in a game with seven or more players from your friends list.
Earn silver medals on all Portal challenges.
Earn gold medals on all Portal challenges.
Earn bronze medals on all Portal challenges.
Accumulate 1000 total kills.
Accumulate 10 turret kills with a single turret.
Trick an opposing medic into healing you.
Get 25 headshots as a Sniper.
Get five kills in a row without dying.
Set five enemies on fire in 30 seconds.
Get five revenge kills.
Win 20 games.
Send the garden gnome into space.
Continue playing to unlock this secret achievement.
Save all buildings outside the missile silo from destruction.
Beat DOG in a race to the White Forest base.
Find every radar cache in chapter Under The Radar.
Unlock the rocket launcher lambda cache in chapter Under The Radar.
Run over 20 enemies with the car in Episode Two.
Defeat the chopper in Episode Two without any misses.
Kill a Hunter with its own flechettes.
Squish every antlion grub in Episode Two.
Find and break every web cache in Episode Two.
Help Griggs and Sheckley hold off the antlion invasion inside the mine shaft.
Kill an acid antlion worker.
Use flares to light 15 zombies on fire.
Beat Episode One firing exactly one bullet. Grenade, crowbar, rocket, and Gravgun kills are okay!
Escape City 17 with Alyx.
Don't let any citizens die when escorting them to the escape train.
Destroy the gunship in the hospital attic.
Help Alyx snipe 30 enemies in Episode One.
Survive long enough to get on the parking garage elevator.
Use the cars to squash 15 antlions in Episode One.
Steal a Zombine's grenade.
Contain the Citadel core without killing any stalkers.
Contain the Citadel core.
Make it to the bottom of the Citadel's main elevator shaft in one piece.
Find all lambda caches in Half-Life 2.
Kill five enemies with the same energy ball.
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Survive the rooftop strider battle in the ruins of City 17.
Shut down the supression device by disabling its generators.
Kill an Elite Soldier with his own energy ball.
Kill all of the snipers in City 17.
Survive the generator plaza standoff in chapter Anticitizen One.
Get through the toxic tunnel under City 17 in Half-Life 2.
Kill an enemy by planting a hopper mine.
Gain command of a squad of rebels in the uprising.
Survive the second turret standoff in Nova Prospekt.
Kill five enemies with a Manhack.
Kill an enemy with a toilet.
Destroy six gunships in Half-Life 2.
Use the antlions to kill 50 enemies.
Cross the antlion beach in chapter Sandtraps without touching the sand.
Kill a Combine soldier with his own grenade.
Pin a soldier to the billboard in chapter Highway 17.
Kill 3 enemies using the crane.
Play through Ravenholm using only the Gravity Gun.
Kill 30 enemies with thrown physics objects.
Use DOG's ball to make a basket in Eli's scrapyard.
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Get the Gravity Gun in Black Mesa East.
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Destroy the hunter-chopper in Half-Life 2.
Get the airboat's mounted gun.
Get the airboat.
Kill five barnacles with one barrel.
Get the crowbar.
Break the mini-teleporter in Kleiner's lab.
Escape the apartment block raid.
Accumulate 25000 heal points as a Medic.
Play a complete round with every class.
Play a complete game on every map.
Successfully defend Gravel Pit without giving up a capture.
Successfully defend Dustbowl without giving up a capture.
Win Hydro without giving up a capture.
Win Well in 5 minutes or less.
Win 2Fort with a shutout.
Beat all six Portal advanced maps.
Beat four Portal advanced maps.
Beat two Portal advanced maps.
Jump 300 feet.
Detach security cameras from the walls.
Complete Portal.
Make the correct party escort submission position decision.
Do whatever it takes to survive.
Knock down a turret with another turret.
Fall 30,000 feet.
Acquire the fully powered Aperture Science Handheld Portal Device.
