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