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