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