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