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