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