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