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