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