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