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