Horse artillery was a type of light, fast-moving, and fast-firing field artillery that consisted of light cannons or howitzers attached to light but sturdy two-wheeled carriages called caissons or limbers, with the individual crewmen riding on horses. This was in contrast to other forms of field artillery which may also be horse-drawn but were heavier and whose gunners either marched on foot or were transported seated on the gun carriage, wagons or limbers. Horse artillery units provided highly mobile fire support especially to cavalry units, and existed in armies in Europe, the Americas, and Asia, from the early 17th to the mid-20th century.

Once in position, horse artillery crews were trained to quickly dismount, deploy or unlimber their guns (detach them from their caissons), then rapidly fire grapeshot, shells or round shot at the enemy. They could then just as rapidly limber-up (reattach the guns to the caissons), remount, and be ready to move to a new position, similar to the shoot-and-scoot tactics of their modern counterparts.

Horse artillery was highly versatile and often supported friendly cavalry units by disrupting enemy infantry formations such as infantry squares with rapid concentrated fire. This would leave the enemy infantry vulnerable to cavalry charges. Their mobility also enabled them to outmaneuver enemy foot artillery units, and to act as a rearguard (in concert with friendly cavalry) to cover the retreat of slower units. A full battery could have a combined front of riders over 50 men strong. If the horse artillery was mistaken for cavalry, the enemy might receive an unpleasant surprise when the towed batteries wheeled around, unlimbered, loaded, sighted and opened fire. Highly proficient batteries could do so in less than a minute.

Essentially a hybrid of cavalry and artillery, irregular horse artillery units were first used by Sweden in the 17th century during the Thirty Years' War by Lennart Torstensson. Torstensson was the artillery expert of Gustavus Adolphus of Sweden, and used them to provide cavalry with the fire support it needed to deal with massed infantry formations without sacrificing their speed and mobility. Gustavus Adolphus had previously tried intermixing infantry units with cavalry, and this was somewhat successful since the cavalry at that time did not charge the enemy at full gallop.

Others tried to combine firepower with mobility by using novel cavalry tactics such as the caracole, but these slowed the cavalry down and proved largely ineffective. The best solutions involved creating hybrid units of mounted infantry, most notably dragoons. Although they proved highly useful and versatile troops, whether they fired mounted or dismounted, they still had to slow down or at least stop temporarily, thereby losing their main advantages as cavalry.

In the early 18th century the Russian army began equipping cavalry formations with small units of light horse artillery equipped with 2-pound cannons, and portable 3-pound mortars which were transported on horseback (the weights refer to the size of the projectiles, not the artillery pieces.) Though not decisive by themselves, these units inflicted losses on Prussian troops and influenced Frederick the Great to form the first regular horse artillery unit in 1759.

Frederick understood that the greatest threat to massed infantry was concentrated artillery fire. He realized that even small and relatively light guns could severely disrupt or destroy infantry units if they could be brought in close enough and fire often enough. But since even light foot artillery travelled at the speed of a marching soldier, the solution was to make every artilleryman a part-time horseman. Through relentless drill and discipline Frederick emphasized mobility and speed in all phases of their operations. The unit consisted of a battery of six 6-pound cannons with 48 men, including 3 officers. The battery was wiped out and reformed twice in that same year at the Battle of Kunersdorf and the Battle of Maxen. Despite the setbacks, the new arm had proved so successful that it was quickly reorganized and by the start of the French Revolutionary Wars in 1792 consisted of three companies of 605 men, with batteries consisting of eight 6-pound guns and one 7-pound mortar each.

French artilleryman, engineer and general Jean-Baptiste de Gribeauval had served with the military mission to Prussia, as well as fighting against Frederick in the Seven Years' War. After that war he made numerous technical improvements to French cannons which made them lighter, faster and much easier to aim. These improvements proved a great advantage to horse artillery as well. Later, the British army officer Henry Shrapnel invented a deadly new type of ammunition that was put to effective use by horse artillery units.