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