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