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