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