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