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