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