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