There were three main troop types in Irish warfare through the (later) middle ages and Early Modern period: the Irish chiefs or nobles, the gallowglass mercenaries, and the kerne. Anglo Normans also joined the Irish wars, originally fighting as familiar knights, but over time they assimilated to the conditions of Ireland.

The Irish nobles largely fought as light horsemen, the 'horse boys' of Irish armies, wearing little armor, riding without much tack or saddlery (including stirrups), and relying on javelins as their main weapon. They were well suited to harassment and pursuit over rough terrain.

The galloglass were originally Scottish mercenaries who settled in Ireland, with Irish imitating their way of fighting. Armed with large axes (sparths) or swords, they were heavy infantry who specialized in the charge; mail armor was common. On campaign, they were accompanied by a servant to carry armor and a boy to carry provisions; they also carried darts or javelins for their master to throw before charging. In many ways, they were the core of the army, whose efforts were expected to decide the battle. The 16th century shift to pikes left them behind, but they remained handy fighters into the century.

Lastly, the kerne were mostly poor peasants, obligated to fight for their chiefs. They were light foot, armed with some combination of swords, shields, bows, and javelins; they largely could not afford heavy weapons. Later, many adopted firearms as their main weapon. Some of them became more professional, being retained full time by their patrons who quartered them on the peasantry.

The predominant form of warfare in Ireland was cattle raiding, in which small groups of men snuck up on their enemies' herds and ran them off, driving them towards their own territory. To ensure their own safety against raiders, the Irish chiefs had defensible tower houses. To defend these structures and to pursue cattle raiders, they had always-ready gallowglass as well as their own horse and perhaps some more permanent kerne.