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