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