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