In the 21st century the Romance languages are all written in the Latin alphabet, with certain modifications, though until the mid-19th century Romanian was normally written in Cyrillic (used in Moldova until 1989), and, in the Middle Ages, Arabic script was used for some Spanish dialects.

As soon as scribes first made attempts to write in vernacular languages, they found the resources of the Latin alphabet inadequate to represent the non-Latin sounds of their spoken language. One device used to overcome those difficulties was the addition of the letter h to another, to indicate a deviant pronunciation: thus, ch might represent the /ch/ sound in Spanish (e.g., muchacho ‘boy’) or the /sh/ (earlier /ch/) sound in French (e.g., chef ‘chief’). C would normally be used for the /k/ sound (before a, o, u) or an /s/ or /th/ sound (before i, e). In Italian, conversely, ch serves to distinguish the /k/ sound, followed by e, from the /ch/ sound (compare che /ke/ ‘that, who’ with c’è /che/ ‘there is’). H was also sometimes added to n and l to indicate a palatal pronunciation (similar to the ny in English canyon and li in scallion), as today in Portuguese vinho ‘wine’ and filho ‘son.’ The palatal consonants n and l are also often depicted by doubled letters or other combinations of letters: the palatal n as nn (or its scribal variant ñ), gn, nj, or in; palatal l as ll, gl, lj, il, or yl, as well as the combinations nh and lh, already mentioned. Another device frequently used to stretch the capacity of the Latin alphabet was to distinguish the letters i and j, u and v, which were originally each single letters i (with variant form j) and v (with variant form u, and in Latin pronounced u or w). In Romance, v and j came to represent consonants, while u and i retained their vowel values.

The Latin letter x, an abbreviation for ks, was also put to other uses in Romance; in Portuguese, Catalan, Sicilian, and Old Spanish it represents a /sh/ sound, in modern Spanish a strong /h/ sound, more commonly spelled with a j, and in northern Italian dialects, the /z/ sound. Other letters pressed into use for new consonantal sounds were z (used in Italy for /ts/ and /dz/ sounds), Germanic k and w, and the Visigothic ç (for /ts/ and sometimes /s/, as today in French and Portuguese).

Vowels were less of a problem for early Romance scribes—diphthongs were simply shown as vowel combinations such as ie, uo. Later, the diaeresis (¨) was sometimes introduced to distinguish diphthongs from adjoining vowels that were to be pronounced separately. Non-Latin vowels are rarely clearly distinguished: French u (pronounced like German ü), for instance, was written u and not consistently distinguished from Latin u (pronounced as in English lunar and, in modern French, written ou). Nasal vowels in French are marked by a following n or m; in Portuguese a tilde is often used for final nasal vowels and diphthongs (ã, ãi). Use of diacritics was not consistent until modern times; thus, so-called long and short e, still not always distinguished in Italian, are shown as é and è or ê (e.g., élève ‘student’) in French (since the 18th century) and as e and é in Portuguese (since about 1930). Romanian established the use of î, â, and ă only in the 20th century.

In most of the languages with a long history of writing, the original attempts by scribes at phonological transcription were followed by an “etymological” period in which Latinized spelling gained ground. Castilian was least subject to this fashion, and, because its phonology has changed comparatively little since the Middle Ages (when its spellings became more or less fixed), it has few orthographic problems today. Standard Italian retains a fairly etymological orthography that covers up various minor regional differences of pronunciation; small reforms have been made through the centuries (in the 17th century, for instance, the use of h—except in ho, ha, hanno—was discontinued; in the 20th century, î and j for ii, as in studii, virtually disappeared), but chaos still reigns in the 21st century in the use of accents. Romanian suffered from etymologizing orthography in the 19th century, but successive edicts of the Romanian Academy, of which the most important was dated 1932, have established a more-or-less-phonetic spelling (the notable exception being the depiction of final “soft” consonants by a following i). Modern Catalan, like other “minor” languages, had the aid of expert linguists in the establishment of its orthography. A standard was proposed by Antonio María Alcover Sureda, a Catalan priest, philologist, and writer from Majorca, in 1913, which is accepted, with small variations, by most writers.

Only two Romance languages, French and Portuguese, have had major orthographic problems, mainly resulting from the radical transformations that have affected their phonology since the Latin period. Portuguese attempted to overcome its difficulties by a series of governmental reforms during the 20th century, but, in spite of official agreements between Portugal and Brazil in 1931 and 1945, there was little consistency in usage, with Brazilian writers, especially, remaining more conservative (i.e., etymological). In 2008, however, the Portuguese parliament passed an act mandating the use of a standardized orthography based on Brazilian forms. In France, in spite of vociferous demands for reform since the 16th century, only minor changes have been accepted (usually originally from unofficial sources, such as printers), so that French orthography today reflects 12th-century phonology, overlaid by the etymologizing of Middle French legal scribes. Battles still rage between the reformers, who deplore the absurdly large proportion of school time devoted to teaching spelling, and the defenders of tradition, who point out that the phonological character of French, with no consistent phonetic markers for the word, make it unsuitable for phonetic transcription and that written French has its own structure, not identical with that of the spoken language.