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