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