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