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