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