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