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