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