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