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