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