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