The Roman alphabet was introduced with Christianity about the year 1000, but the older ð (eth, or voiced th) and þ (thorn, or unvoiced th) were retained, as were æ and ö. The vowels may also take acute accents: á, é, í, ó, ú, and ý.

The Icelandic phonetics contains some interesting features, also sometimes seen in Faroese, like the so-called preaspiration: the process under which the word nytt will be read as [nuht]. Modern Icelandic, which is considered to date from 1540, when the New Testament was translated, is still heavily inflected, unlike the other Scandinavian languages. Icelandic has three genders and four cases of nouns, pronouns, and adjectives; verbs have three persons. The language is equally purist in vocabulary. Linguistic policy formulated in the 18th century generally prevents assimilation of foreign words, so that instead of international scientific and technological terms being adopted, for example, compounds of native Icelandic words are formed; in addition, old words are revived and new ones are created, based on native roots.