In Ireland, English and Irish have been in contact for centuries and influenced each other mutually. Nowadays, English is the dominant language on the island, but in a distinctive variation that shows influences of the Irish language: Irish English. The main objective of this thesis is to find systematic correspondence between the frequency of these reflexes of Irish in Irish English and the medium and the degree of formality of the registers these reflexes are contained in. To this end, eleven features of Irish English that originated from contact with Irish were selected and extracted from the Ireland Compartment of the International Corpus of English. The number of
these occurrences in each register of the corpus was then put into relation with the medium (spoken or written) and the formality of the register. To determine the formality of a register, a scale of formality based on the situational characteristics of the language production event was created, ranging from 0 for least formal to 12 for most formal. The main findings of this analysis were firstly that the number of Irish English features is higher in spoken than in written registers. Secondly, reflexes of Irish in Irish English are more frequent in informal than in formal registers: the more formal a register is, the fewer Irish influences will be found in it.