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