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