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