Ammunition (noun, commonly shortened to ammo) is the general term used for the material fired, scattered, dropped or detonated from any weapon. The term ammunition can be traced back to the mid-17th century. Broadly speaking, ammunition refers to both expendable weapons (e.g., bombs, missiles, grenades, land mines, naval mines and anti-personnel mines) and the component parts of other weapons that create the effect on a target (e.g., bullets and warheads). Nearly all mechanical weapons require some form of ammunition to operate. The word comes from the French la munition, which refers to the material used for war. The terms ammunition and munitions are often used interchangeably, although the term munition now usually refers to the actual weapons system with the ammunition required to operate it.

The purpose of ammunition is to project a force against a selected target to have an effect (usually, but not always, lethal). The most iconic example of ammunition is the firearm cartridge, which includes all components required to deliver the weapon effect in a single package.

Ammunition comes in a great range of sizes and types and is often designed to work only in specific weapons systems. However, there are internationally recognized standards for certain ammunition types (e.g., 5.56×45mm NATO) that enable their use across different weapons and by different users. There are also specific types of ammunition that are designed to have a specialized effect on a target, such as armor-piercing shells and tracer ammunition, used only in certain circumstances. Ammunition is commonly colored in a specific manner to assist in the identification and to prevent the wrong ammunition types from being used accidentally.