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