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