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