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