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