The SPAS-12 was designed during the 1970s as a semi-automatic military/law enforcement shotgun. Introduced to the United States in 1983, where it was marketed as a sporting shotgun to help bypass laws that would normally label it as illegal for private ownership. As a result, the SPAS acronym officially stands for "Sporting Purpose Automatic Shotgun". However, military-oriented features like a heavy heat shield for sustained fire increase the weight of the weapon to the point it becomes unwieldy for hunting or competition shooting, although its looks have made it a favourite of  Hollywood .

The SPAS-12 has two settings; automatic (more accurately, self-loading semi-automatic) - the foregrip is locked forward and a gas system serves to load the next round without further effort from the operator, or pump-action - the foregrip must be manually pumped back and forth after every shot to eject the spent shell and load a new round from the internal magazine. This mode is required to reliably fire low-pressure ammunition such as tear gas rounds or bean bags. Switching between firing modes is done by pressing a button under the foregrip, and sliding the foregrip slightly forwards or backwards until it clicks into position. The SPAS-12 also has a magazine cut-off feature that, when activated, prevents the loading of a new round from the internal magazine when the slide is opened. This allows the operator to load a specialized round into the chamber without going through the entire magazine first. Fitted with post front/open notch rear sight.