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