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