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