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