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