The Gallowglass (also spelled galloglass, gallowglas or galloglas; from Irish: gallóglaigh meaning "foreign warriors") were a class of elite mercenary warriors who were principally members of the Norse-Gaelic clans of Ireland and Scotland between the mid 13th century and late 16th century. It originally applied to Highland Scots, who shared a common background and language with the Irish, but as they were descendants of 10th-century Norse settlers who had intermarried with the local population in western Scotland, the Irish called them Gall Gaeil ("foreign Gaels").
An early family of gallowglasses was the MacSweeneys, settled by the O'Donnells in north Donegal. These were followed by MacDonnells, MacAlisters, MacCabes and several other groups settled by powerful Irish nobles in different areas. The gallowglasses were attractive as heavily armoured, trained infantry to be relied upon as a strong defence for holding a position, unlike most Irish foot soldiers, who were less well armoured than the typical Irish noble who fought as cavalry.