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