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