Break-action
A view of the break-action of a typical double-barrelled shotgun, shown with the action open
For most of the history of the shotgun, the break-action breech loading double was the most common type, typically divided into two subtypes: the traditional "side by side" shotgun features two barrels mounted one beside the other (as the name suggests), whereas the "over and under" shotgun has the two barrels mounted one on top of the other. Side by side shotguns were traditionally used for hunting and other sporting pursuits (early long barreled side-by side shotguns were known as Fowling Pieces for their use hunting ducks and other birds), whereas over and under shotguns are more commonly associated with sporting use (such as clay pigeon/skeet shooting). Both types of double-barrel shotgun are used for hunting and sporting use, with the individual configuration largely being a matter of personal preference.
Another, less commonly encountered type of break-action shotgun is the combination gun, which is an over and under design with one shotgun barrel and one rifle barrel (more often rifle on top, but rifle on bottom was not uncommon). There is also a class of break action guns called drillings, which contain three barrels, usually 2 shotgun barrels of the same gauge and a rifle barrel, though the only common theme is that at least one barrel be a shotgun barrel. The most common arrangement was essentially a side by side shotgun with the rifle barrel below and centered. Usually a drilling containing more than one rifle barrel would have both rifle barrels in the same caliber, but examples do exist with different caliber barrels, usually a .22 Long Rifle and a centerfire cartridge. Although very rare, drillings with three and even four (a vierling) shotgun barrels were made.