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