A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellants to launch a projectile. Cannon vary in caliber, range, mobility, rate of fire, angle of fire, and firepower; different forms of cannon combine and balance these attributes in varying degrees, depending on their intended use on the battlefield. The word cannon is derived from several languages, in which the original definition can usually be translated as tube, cane, or reed. The plural of cannon is also cannon in British English, but in American English, cannons is generally preferred. In the modern era, the term cannon has fallen into decline, replaced by "guns" or "artillery" if not a more specific term such as "mortar" or "howitzer", except for in the field of aerial warfare, where it is usually shorthand for autocannon.

First used in China, cannon were among the earliest forms of gunpowder artillery, and over time replaced siege engines—among other forms of aging weaponry—on the battlefield. In the Middle East, the first use of the hand cannon is argued to be during the 1260 Battle of Ain Jalut between the Mamluks and Mongols. The first cannon in Europe were probably used in Iberia in the 11 and 12th centuries, and English cannon were first deployed in the Hundred Years' War, at the Battle of Crécy, in 1346. On the African continent, the cannon was first used by the Somali Imam Ahmad ibn Ibrihim al-Ghazi of the Adal Sultanate in his conquest of the steppes of Ugaden in 1529. It was during this period, the Middle Ages, that cannon became standardized, and more effective in both the anti-infantry and siege roles. After the Middle Ages most large cannon were abandoned in favor of greater numbers of lighter, more maneuverable pieces. In addition, new technologies and tactics were developed, making most defences obsolete; this led to the construction of star forts, specifically designed to withstand artillery bombardment though these too (along with the Martello Tower) would find themselves rendered obsolete when explosive and armour piercing rounds made even these types of fortifications vulnerable.