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