Here is the full list of all 73 Left 4 Dead achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Earn a Gold medal on every official Survival level.
Earn at least a Silver medal on every official Survival level.
Earn at least a Bronze medal on every official Survival level.
Your team wipes all Survivors after the escape vehicle has opened in Crash Course.
Kill 53,595 Infected.
As A Tank hit 20 Survivors with a car in the Crash Course campaign.
Win a Versus campaign of Crash Course.
Pounce a Survivor for 25 points of damage in the Crash Course campaign.
Dole out 5000 total Survivor damage as a Special Infected.
Complete one round of Survival on The Last Stand.
Survive the Crash Course Campaign.
Kill 5,359 Infected in the Crash Course campaign.
Stun a Tank with an explosion in the Crash Course campaign.
Restart the generator within 30 seconds of it shutting off.
As an Infected, incap a Survivor who has entered and left a safe room.
Leave a safe room to save an incapped teammate and bring them back safely.
As a Special Infected, incap someone who is trying to sacrifice themselves.
Complete "The Sacrifice".
Have Bill sacrifice himself for the team.
Protect any Survivor from an attacking Infected 50 times.
Have all 3 generators running at once in "The Sacrifice" finale.
Catch a rare strain of infection, then pass it on to someone else.
Headshot a Hunter while he's leaping.
Kill a Special Infected with an exploding barrel.
Kill an Infected with a single blow from behind.
Make 100 headshot kills.
Set 101 Infected on fire.
Save another Survivor from a Special Infected while on the ground.
Kill a Witch with a single headshot.
Kill a Witch without any Survivor taking damage from her.
Rescue a Survivor from a Smoker's tongue before he takes damage.
Survive all campaigns on Expert.
Survive the No Mercy campaign.
Revive 50 incapacitated Survivors.
Rescue a Survivor trapped in a closet.
Sneak past all Witches in a campaign without disturbing one.
Beat a campaign with all 4 Survivors.
Survive the Blood Harvest campaign.
No Survivors take damage after contacting the rescue vehicle.
Heal 25 Survivors with a first aid kit.
Punch a Hunter as he is pouncing.
Heal a fellow Survivor when your own health is below 10.
Kill 10 Smokers as they are pulling helpless Survivors.
You or another Survivor take no damage after being vomited on by a Boomer.
Shove a Boomer and then kill him without him splashing on anyone.
Play an entire campaign with no Survivors taking friendly fire damage.
Survive any campaign on Expert.
Survive a campaign with no Survivors taking damage from Special Infected.
All Survivors complete a campaign without being vomited on.
Survive the Dead Air campaign.
Kill a Smoker who has grabbed you with his tongue.
Kill 1000 Infected with a mounted machine gun.
Light a Tank with a Molotov.
Light a Witch with a Molotov.
Earn a Gold medal in Survival mode on any official level.
Earn a Silver medal in Survival mode on any official level.
Earn a Bronze medal in Survival mode on any official level.
Survive an entire campaign using only pistols.
Finish a campaign without ever using a first aid kit on yourself.
Survive a campaign without being incapacitated.
Survive the Death Toll campaign.
Single-handedly kill a Tank.
Kill a Tank without it dealing any damage to a Survivor.
Give pain pills to 10 Survivors.
Blow up 20 Infected in a single explosion.
Shove a Hunter off of a pinned and helpless Survivor.
Drag a Survivor 100 feet with your tongue as a Smoker.
Constrict two Survivors on one life as a Smoker.
Smoker pull a bile-covered Survivor until you hold him during Crash Course.
Pounce two different Survivors on one life as a Hunter.
Cover four Survivors with Boomer bile at once.
Kill all four Survivors on one life as a Tank.
Your team incapacitates three Survivors within five seconds.