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