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