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