Code-mixing and code-switching are common and well-documented processes in the speech of multilingual persons. Where multilingual persons are also literate in each language, code-mixing is also possible in writing. Despite conservative pressures which tend to deem only one of the languages in a linguistic repertoire the prestige variety, and therefore the primary choice for written expression, multiliterate authors who are able to assume a multiliterate readership may use two or more languages in their texts. Some theories of code-mixing are here summarized, along with a review of code-mixing in spoken Irish. Examination of code-mixing in modern and contemporary Irish literary texts shows that, structurally, written code-mixing is for the most part similar to what is observed in spoken language. Functionally, however, written mixing often has wider aims. Because writing is a planned and conscious form of language, multilingual writers utilize their greater linguistic repertoires strategically by imbuing different languages with different symbolic meanings. A full appreciation of such texts requires an understanding not just of the languages involved, but also of their functions in the cultural environment and the historical, political, and cultural associations with the other languages.