Mór ("big") and Óg ("young") are used to distinguish parent and child, like "senior" and "junior" are used in English, 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 original Ó).
Adjectives denoting hair colour may also be used, especially informally, e.g. Pádraig Rua ("red-haired Patrick"), Máire Bhán ("fair-haired Mary").
If the mother's name is used, then the maternal grandfather or grandmother may follow it, e.g. Máire Sally Eoghain.
A man's surname is generally formed by Ó ("descendant"; historically Ua) or Mac ("son") followed by a name or definite noun (often a profession) in the genitive case, e.g. Ó Dónaill (literally "descendant of Dónall") and Mac Siúrtáin (literally "son of Jordan").
In Ulster it is common for a woman who adopts her husband name to just use Ní or Nic rather than the forms seen below.
Some names consist of Mac Giolla ("servant's son") or Ó Maoil ("follower's descendent") followed by a name in the genitive case, e.g. Mac Giolla Phádraig, Ó Maoil Eoin.