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