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