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