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