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