Gun

The main weapons in Left 4 Dead are divided into two tiers. The first is available to every Survivor when the scenario starts. Weapons in the second tier can be found throughout the maps and at the end of the scenario, just before the Finale. All weapons can be used to melee Infected within close combat, pushing them back.

There is currently no way to distribute weapons or ammunition among teammates. All weapons have an attached flashlight with an unlimited battery; however, the flashlight's beam is only visible to the player using that particular flashlight if the other player's game settings are set too low.

Picking up either tier of weapon from a table or other location holding new weapons (not from a dead Survivor) provides a full ammo refill, equivalent to interaction with an ammo pile.

Note: Weapons will continue reloading despite the lack of reloading animation during melee attacks, provided that reloading starts before the melee attacks. This is extremely useful if out of ammo, or both primary and pistol need to be reloaded as it allows the player to shove back attacking Infected while their weapon reloads in the background. When it is fully reloaded (after 2-3 melees' time) it can be used to kill the staggering Infected.

Tier 1
Each of the Survivors has the choice of starting with one of either of the first tier weapons, but they can switch or restock ammo on checkpoints.

Tier 2
Each of the Survivors have the choice of switching their first tier weapons to one of these on later checkpoints. Picking a Tier 2 weapon up will automatically fill the reserve ammo.

Unknown Tier Weapons
These weapons has been seen in the Left 4 Dead 2 footage, it's unknown if only these weapons can use Incendiary Ammunition to allow the weapons to set Infected on fire or all the weapons.

Sidearm
Each of the Survivors starts with a pistol.
 * Pistol
 * Dual Pistols (Acquired when a second pistol is picked up.)

Grenades
Each of the Survivors can carry either one Molotov cocktail or one pipe bomb.
 * Molotov cocktail
 * Pipe bomb

Usable Items
These items found in various places in campaigns and be carried, once carried the character cannot use any other weapons until throw or dropped, you can also use this weapon to push back infected.
 * Gas can
 * Oxygen tank
 * Propane tank

Other

 * Minigun

Trivia

 * Most of the weapons in the game are based off of the weapons in another Valve game, Counter-Strike.
 * The flashbang grenade was rumored to have been made a weapon at some point, which would have stunned all nearby Infected. This would make sense since almost all of the weapons in Left 4 Dead seem to based on weapons in Counter-Strike. However, this is no proof in the game files that a flashbang grenade ever existed.
 * The posters before each level sometimes show characters with scoped MP5's, but they are not usable in the actual game.