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