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