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A formalIrish name consists of agiven name and asurname. In theIrish language, most surnames arepatronymic surnames (distinct frompatronyms, which are seen inIcelandic names for example). The form of a surname varies according to whether its bearer is a man, a woman, or a woman married to a man, who adopts his surname.

An alternative traditional naming convention consists of the first name followed by a double patronym, usually with the father and grandfather's names. This convention is not used for official purposes but is generalized inGaeltachtaí (Irish-speaking areas) and also survives in some rural non-Gaeltacht areas. Sometimes the name of the mother or grandmother may be used instead of the father or grandfather.

A first name may be modified by an adjective to distinguish its bearer from other people with the same name.Mór ("big") andÓg ("young") are used to distinguish parent and child, like "senior" and "junior" are used inEnglish, but are placed between the given name and the surname, e.g.Seán Óg Ó Súilleabháin corresponds to "John O'Sullivan Jr." (anglicised surnames often omit⟨O'⟩, leaving no trace of originalÓ).

The wordBeag ("little") can be used in place ofÓg. This does not necessarily indicate that the younger person is smaller in stature, merely younger than their parent or in some cases to imply a baby was small, possiblypremature, at birth.

Adjectives denoting hair colour may also be used, especially informally, e.g.Pádraig Rua ("red-haired Patrick"),Máire Bhán ("fair-haired Mary").

Colloquially inGaeltachtaí (Irish-speaking areas) and some other areas it remains customary to use a name formed by the first name (or nickname), followed by the father and the paternal grandfather's name, both in thegenitive case, e.g.Seán Ó Cathasaigh (Seán O'Casey), son ofPól, son ofSéamus, would be known to his neighbours asSeán Phóil Shéamuis. Occasionally, if the mother or grandmother was a well-known person locally, her name may be used instead. If the mother's name is used, then the maternal grandfather or grandmother may follow it, e.g.Máire Sally Eoghain.

This system can be particularly useful for distinguishing people who live in the same area and who share a common surname but are not closely related, e.g. two people named John McEldowney might be known as "John Patsy Dan" and "John Mary Philip" respectively. Even the Irish forms sometimes survive in parts of theSperrins, so that among the principal families ofGlenullin some branches are known by father/grandfather forms such asPháidí Shéamais orBhrian Dhónaill.

A man's surname is generally formed byÓ ("descendant"; historicallyUa) orMac ("son") followed by a name or definite noun (often a profession) in thegenitive case, e.g.Ó Dónaill (literally "descendant ofDónall") andMac Siúrtáin (literally "son of Jordan"). WhenÓ is followed by a vowel, a (lowercase)⟨h⟩ is attached to the vowel, e.g.Ó hUiginn (O'Higgins) orÓ hAodha (Hughes).

A woman's surname replacesÓ withNí (reduction ofIníon Uí "descendant's daughter") andMac withNic (reduction ofIníon Mhic "son's daughter"). In both cases the following name undergoeslenition, except for whenNic is followed by⟨c⟩ or⟨g⟩. Thus the daughter ofSeán Ó Dónaill has the surnameNí Dhónaill and the daughter of aPól Mac Siúrtáin has the surnameNic Shiúrtáin. InUlster it is common for a woman who adopts her husband name to just useNí orNic rather than the forms seen below.

If a woman marries a man, she may choose to take his surname. In this case,Ó is replaced byBean Uí ("descendant's wife") andMac byBean Mhic ("son's wife"). In both casesBean may be omitted, which results inUí orMhic. In both cases the following name undergoeslenition, except for whenMhic is followed by⟨c⟩ or⟨g⟩. Thus a woman marryingSeán Ó Dónaill may choose to adoptBean Uí Dhónaill orUí Dhónaill as her surname and a woman marryingPól Mac Siúrtáin may choose to adoptBean Mhic Siúrtáin orMhic Siúrtáin as her surname.

Mag,Nig, andMhig are sometimes used instead ofMac,Nic, andMhic before a vowel or⟨fh⟩ (which is silent) followed by a vowel.

Norman surnames formed byde (always lowercase; "of") followed by a name, e.g.de Búrca (Burke),de Paor (Power), orde hÍde (Hide,Hyde).

Some names consist ofMac Giolla ("servant's son") orÓ Maoil ("follower's descendant") followed by a name in the genitive case, e.g.Mac Giolla Phádraig,Ó Maoil Eoin.

Many Irish people useEnglish (oranglicised) forms of their names in English-language contexts andIrish forms in Irish-language contexts. The Irish names of some people more famous under their English names include:

Other people are generally better known by their Irish name than by their English name, including the following:

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• List of Irish-language given names
• Celtic onomastics
• Place names in Ireland
• Scottish Gaelic name
• Welsh surnames

• Names - Nualeargas
• Irish Names at LibraryIreland.com
• The Origins of Irish Surnames at IrishTimes.com (Archive)
• Find Irish Family Names at Dubliner.com
• 16th & 17th Century Anglicized Irish Surnames from Woulfe by MedievalScotland.org

• Irish language
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