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.
Survive a campaign with no Survivors taking damage from Special 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 53,595 Infected.
Kill 5,359 Infected in the Crash Course campaign.
Have all 3 generators running at once in "The Sacrifice" finale.
Earn a Gold medal in Survival mode on any official level.
Kill 1000 Infected with a mounted machine gun.
Survive all campaigns on Expert.
Survive the Dead Air campaign.
Earn a Silver medal in Survival mode on any official level.
Earn a Bronze medal in Survival mode on any official level.
Survive the Death Toll campaign.
Revive 50 incapacitated Survivors.
Survive the Blood Harvest campaign.
Survive any campaign on Expert.
Smoker pull a bile-covered Survivor until you hold him during Crash Course.
Catch a rare strain of infection, then pass it on to someone else.
Headshot a Hunter while he's leaping.
As A Tank hit 20 Survivors with a car in the Crash Course campaign.
Your team incapacitates three Survivors within five seconds.
Single-handedly kill a Tank.
Pounce a Survivor for 25 points of damage in the Crash Course campaign.
Pounce two different Survivors on one life as a Hunter.
Your team wipes all Survivors after the escape vehicle has opened in Crash Course.
Win a Versus campaign of Crash Course.
As an Infected, incap a Survivor who has entered and left a safe room.
Leave a safe room to save an incapped teammate and bring them back safely.
Survive a campaign without being incapacitated.
Kill 10 Smokers as they are pulling helpless Survivors.
Complete one round of Survival on The Last Stand.
Play an entire campaign with no Survivors taking friendly fire damage.
All Survivors complete a campaign without being vomited on.
No Survivors take damage after contacting the rescue vehicle.
Kill a Special Infected with an exploding barrel.
Heal 25 Survivors with a first aid kit.
Kill a Witch with a single headshot.
Rescue a Survivor trapped in a closet.
Survive an entire campaign using only pistols.
Sneak past all Witches in a campaign without disturbing one.
Survive the Crash Course Campaign.
Give pain pills to 10 Survivors.
Protect any Survivor from an attacking Infected 50 times.
Stun a Tank with an explosion in the Crash Course campaign.
Kill a Witch without any Survivor taking damage from her.
Complete "The Sacrifice".
Have Bill sacrifice himself for the team.
Set 101 Infected on fire.
Shove a Hunter off of a pinned and helpless Survivor.
Punch a Hunter as he is pouncing.
Finish a campaign without ever using a first aid kit on yourself.
Survive the No Mercy campaign.
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.
Kill a Smoker who has grabbed you with his tongue.
Beat a campaign with all 4 Survivors.
Restart the generator within 30 seconds of it shutting off.
Light a Tank with a Molotov.
Light a Witch with a Molotov.
Kill an Infected with a single blow from behind.
As a Special Infected, incap someone who is trying to sacrifice themselves.
Heal a fellow Survivor when your own health is below 10.
Shove a Boomer and then kill him without him splashing on anyone.
Save another Survivor from a Special Infected while on the ground.
Kill all four Survivors on one life as a Tank.
Dole out 5000 total Survivor damage as a Special Infected.
Cover four Survivors with Boomer bile at once.
Constrict two Survivors on one life as a Smoker.
Drag a Survivor 100 feet with your tongue as a Smoker.
Blow up 20 Infected in a single explosion.
Kill a Tank without it dealing any damage to a Survivor.