Not all ancient Irish families have traditional arms recorded in authoritative heraldic sources. The Genealogical Office in Dublin, formerly known as the Office of Arms, is of course the principal source for such information. Grants and even Confirmations of Arms to individual members of a sept do not give to other persons of the same name, not included in the terms of the grant or confirmation, any right to use such arms. There are, however, a number of coats of arms on record which by custom are regarded as appertaining to all members of a sept. At this point it would be well to consider what we mean by the term "sept" - the word "clan" has been avoided because its use might imply the existence in Ireland of a clan system like that so highly developed in Scotland, which in fact we never had in this country. The term "sept" has never, as far as I know, been given an authoritative technical definition. It can perhaps best be explained by saying that it is a collective term describing a group of persons who, or whose immediate and known ancestors, bore a common surname and inhabited the same locality. Some danger exists of persons not of the true ancestry of a sept being inextricably identified with it. There is no doubt that up to the middle of the seventeenth century many of the labouring class had no hereditary surnames. This is referred to here only to indicate a possible objection to a wide interpretation of sept arms, namely that "serfs" (as they have been called in this connection) may, when the practice of using transitory surnames died out, have assumed as their permanent surnames those of their masters, rather in the same way as the slaves of the plantations in the West Indies sometimes assumed planter surnames. While this contention is not without substance, the consensus of opinion is that such assumption was not at all widespread. The elasticity inherent in the concept of sept arms is repugnant to British heraldic practice. In England armorial bearings are held to emanate from the Sovereign and are hereditary, though devoid of sanctions to protect what may be regarded as a family heirloom and personal property; in Scotland the right to bear arms is strictly regulated by law; on the Continent, again, heraldic usage differs considerably from British. Ulster King of Arms (as the head of the Irish Office of Arms in Dublin was called) who derived his authority, like Garter and Lyon, from the King of Great Britain and Ireland, continued to exercise his functions in Ireland until March 31, 1943, when his office was transferred to the Government of Ireland and has since been known as the Genealogical Office, its head being entitled Chief Herald of Ireland. This transfer took place more than twenty years after the establishment of the Irish Free State.
On taking over we were at first inclined to adopt the British attitude in heraldic matters; but after a few years the particular conditions existing in Ireland, politically and historically, induced a modification of outlook, especially in regard to sept arms. In England and Scotland all arms to be found in the records of the heraldic authorities, if not extinct, can be claimed by certain specific individuals. Sept arms, as recorded in the Office of Arms in Dublin Castle somewhat loosely to be regarded as appertaining to all members of the sept. The peculiar circumstances of Ireland, it may be added, were recognised two centuries before the transfer to an Irish authority took place, since Confirmations of Arms, based on use, were issued in Ireland, but not in Great Britain where settled conditions existed. It must be emphasised that the acceptance of the principle of sept arms in no way implies that arms appertain to a surname as such. It does not mean, for example, that every man called Kelly or O'Kelly may legitimately use the well-known arms of O'Kelly of Ui Maine. There were several distinct septs of O'Kelly; and O'Kellys of the Meath or Kilkenny septs have no better title to the said arms than a Murphy or an O'Brien. No one, however, can reasonably object to an O'Kelly taking a proprietary interest in those arms, provided that he is unquestionably of a family originating in the O'Kelly country in Connacht.
Briefly, then, the position is that many Irish coats of arms may be displayed without impropriety by any person of the sept indicated if he really does belong to that sept. Nevertheless anyone wishing to bear arms in the true heraldic sense, e.g. to have them inscribed on silver or seal or in stone carving, would be well advised to apply for a Confirmation of such arms from the Chief Herald of Ireland, which can be obtained at a moderate fee on production of evidence of descent. Corroborative evidence of "user" is also required in all cases where the proof afforded by descent is inadequate. Searches to obtain such evidence are undertaken by the Genealogical Office.
From "More Irish Families" by Edward MacLysaght, the first Chief Herald of Ireland.
The arms to which MacLysaght refers and which fall in the category of sept arms include, but are not limited to the following ...Aherne, McAuliffe, McAuley (McAwley), Barrett (Cork), Barry, O'Beirne, Blake, Boland, Boylan, Boyle, Brady, Brennan (Connacht), Brennan (Ossory), O'Brien, Broder(ick), Browne (Galway), Burke, Butler, Byrne, McCabe, Cahill, Callaghan, McCann, O'Carroll (Ely), McCarten, McCarthy, Casey, Cassidy, Clancy, Clery, Coffey (Cork), Coghlan, Colgan, Concannon, Condon, O'Connell, O'Connor (five septs - Don, Faly, Kerry, Sligo and Corcomroe), Connolly, Conry (Offaly), Conroy (Mulconry, King), Considine, Corrigan, Costello, Cotter, Creagh, Crean, Crowley, Cullane (Collins), Cullen, Cullinan, Curtin, Cusack, Dalton, Daly, Darcy, Davoren, O'Dea, Dempsey, McDermot, Dillon, Dinneen, Doherty, Donlevy, McDonnell (Clare and Connaught), McDonnell (of the Glens), O'Donnell, Donnellon (Donlon), Donnelly, McDonogh, Donohue, Donovan, Doran, O'Dowd, Doyle, Driscoll, Duggan, Dunne, O'Dwyer, Egan, McEnchroe (Crowe), McEniry (Henry), McEvoy, Fagan, Fahy, Fallon, Farrell, Finnegan, Fitzgerald, Fitzgibbon, Fitspatrick, Flaherty, Flanagan, Fleming, Flynn, Fogarty, Fox (from Kearney), French (Galway), Friel, Gallagher, Galvin, O'Gara, McGarry, Garvey, Guinness (McGuinness, Magennis, McGenis), Geoghegan, Geraghty, Gilfoyle, McGillycuddy, Gorman (Mc and O'), Gormley, McGovern (Magauran), Grady,, McGrath, Griffin (O'Griffy), McGuire (Maguire), Hackett, O'Hagan, Halloran, O'Hanlon, Hanly, Hannon, Hanraghty, O'Hara, Hary, Hartagan, O'Hea (Hayes, Hughes), Heffernan, Hegarty, Hennessy, Hynes (O'Heyne, Hynds), Hickey, Higgins (O'Higgin), Hogan, Holohan, Horan, McHugh, Hurley, McInerney, Jordan (McSurtain), Joyce, Kavanagh (Cavanagh), Keane (O'Cahan), Kearney, Keating, O'Keeffe, O'Kelly (Uí Maine), McKenna, Kennedy, Keogh (Connacht), McKeown, Kieran (Kearns), Kinneally (Munster), Kinsella, Kirwan, Lacy (de Lacy), Lally (Mullally), Lawlor (Lalor), O'Leary, Lonergan, O'Loughlin, McLoughlin (formerly O'Melaghlin), McLoughlin (Tirconnel), Lynch (Galway), McLysaght, Madden, McMahon (Oriel), McMahon (Thomond), O'Mahony, O'Malley, Malone, Mangan, McManus, Martin (Galway), Meagher (Maher), O'Meara, Meehan, Molloy (Mulloy), Moloney, Monaghan, Mooney, Moran, O'More (Moore), Moriarty, Moroney, Morris (Morrison, Galway), O'Mullen, Mulvihil, Murphy (Muskerry), Murphy (O'Morchoe, Wexford), McMurrough, Naughton (Naghten), Nagle, McNally, McNamara, Neilon (Nealon), O'Neill, Nolan, Nugent, Phelan (Whelan, Felan), Plunkett, Power, Purcell (of Loughmoe), Quigley (Cogley, Kegley), McQuillan, Quinn (Annaly), Quinn (Thomond), Quinlan, Rafferty, McRannall (Reynolds), Redmond, Regan (Reagan), Reilly, Riordan, Roche, O'Rourke, Ryan (Mulrian), Scanlan, Shanly, Shaughnessy, O'Shea, Sheehan, Sheehy, Sheridan, Shiel (Shields), O'Sullivan Mór, O'Sullivan Beare, Sweeney, Taaffe, McTiernan, O'Tierney, Tobin, O'Toole, Troy (Trehy), Tully (McAtilla), Wall, Walsh (Iverk) and Woulfe.