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