It is the mission of this Y-DNA Geographic project to analyze and sort the descendants of the many mercenary families of Gallowglass (gall oglaigh: foreign soldiers) that came into Ireland between the 13th and 17th centuries from the highlands and western isles of Scotland. It was long thought by scholars that the Irish population merely absorbed the gallowglass over time, it being impossible to tell them apart by the end of gaelic Ireland. It is more than likely that the opposite had occurred more often: the mercenary families absorbed the native Irish. I intend to prove or disprove this theory using genetic genealogy of participants who have highland mercenary surnames, but a genealogical paper trail to Ireland, specifically catholic lines that may pre-date the end of gaelic Ireland circa 1600.