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