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