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