A shotgun shell, shotshell or simply shell is a type of rimmed, cylindrical (straight-walled) cartridges used specifically in shotguns, and is typically loaded with numerous small, pellet-like spherical sub-projectiles called shot, fired through a smoothbore barrel with a tapered constriction at the muzzle to regulate the extent of scattering. A shell can sometimes also contain only a single large solid projectile known as a slug, sometimes fired through a rifled slug barrel. The hull usually consists of a paper or plastic tube often covered at the base by a metallic head cover which retains a primer, and the shot charge is typically contained by a wadding/sabot inside the case. The caliber of the shotshell is known as its gauge.

The projectiles are traditionally made of lead, but other metals such as steel, tungsten and bismuth are also used due to restrictions on lead, or for performance reasons such as achieving higher shot velocities by reducing the mass of the shot charge. Other unusual projectiles such as saboted flechettes, rubber balls, rock salt and magnesium shards also exist. Slug shells can also be made with specialty non-lethal projectiles such as rubber and bean bag rounds.

Shotguns have an effective range of about 35 m (38 yd) with buckshot, 45 m (49 yd) with birdshot, 100 m (110 yd) with slugs, and well over 150 m (160 yd) with saboted slugs in rifled barrels.

Other rounds include:

• Ferret rounds: rounds designed to penetrate a thin barrier (e.g. a car door) and release a gas payload.
• Bolo rounds: two large lead balls attached by a wire.
• Piranha rounds: shells full of sharp tacks.
• Dragon's breath rounds: shells full of incendiary chemicals that creates a fireball/flame when discharged, and can ignite a flammable target at close range.

Most shotgun shells are designed to be fired from a smoothbore barrel, but dedicated shotguns with rifled barrels are limited to lead slugs or sabot slugs as "shot" would be spread too wide by the rifling. A rifled barrel will increase the accuracy of sabot slugs, but makes it unsuitable for firing shot, as it imparts a spin to the shot cup, causing the shot cluster to disperse. A rifled slug uses rifling on the slug itself so it can be used in a smoothbore shotgun.