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