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