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