Rhaeto-Romance, Rheto-Romance, Rhaeto-Italian, or Rhaetian, is a purported subfamily of the Romance languages that is spoken in south-eastern Switzerland and north-eastern Italy. The name "Rhaeto-Romance" refers to the former Roman province of Raetia. The question of whether these languages actually form a subfamily is called the Questione Ladina. The Italian linguist Graziadio Ascoli, writing in 1873, found them to share a number of intricacies and believed they formed a linguistic group. The Rhaeto-Romance languages differ from Italian in their evolution from Latin by having passed through a stage with phonemic vowel length, undergone certain consonant developments, and possibly developed a pair of central rounded vowels (now lost everywhere). If the subfamily is genuine, three languages would belong to it: Romansh in Switzerland, and Ladin and Friulian in Italy. Their combined number of speakers is about 660,000; the large majority of these (about 500,000) speak Friulian.

Before the Roman conquest, the Alps were Celtic-speaking in the north and Rhaetian-speaking in the south. The area was incorporated into the Roman Empire during the reign of Augustus. The Rhaeto-Romance languages originated as a dialect of the provincial Latin of the central Alps.

By the end of the Roman Empire, there was an unbroken region of distinctive Romance speech here, which was gradually fragmented into secluded areas in the high valleys by the encroachment of German dialects from the north and of Gallo-Italic languages from the south.

Rhaeto-Romance was spoken over a much wider area during Charlemagne's rule, stretching north into the present-day cantons of Glarus and St. Gallen, Walensee in the northwest, and Rüthi and the Alpine Rhine Valley in the northeast. In the east, parts of modern-day Vorarlberg were Romance speaking, as were parts of Austrian Tyrol. The northern areas of what is currently Switzerland, called "Lower Raetia" at that time, became German-speaking by the 12th century; and by the 15th century, the Rhine Valley of St. Gallen and the areas around the Walensee were entirely German-speaking.

This language shift was a long, drawn-out process, with larger, central towns adopting German first, while the more peripheral areas around them remained Romansh-speaking longer. The shift to German was caused in particular by the influence of the local German-speaking elites and by German-speaking immigrants from the north, with the lower and rural classes retaining Romansh longer.

The family is most closely related to its nearest neighbors: French, Franco-Provençal, Occitan, Venetian, Istriot and Lombard.

A number of lexical items are shared with Ibero-Romance due to the similar date of Latinization for both regions, although it can also be explained by means of Bartoli's areal linguistics theory, Ibero-Romance being a peripheral area, as are Balkano-Romance, Southern-Italian and Rhaeto-Romance, whereas Gallo-Romance and Italo-Romance are the central area. The Rhaeto-Romance languages were linked to other Romance languages that existed in bordering areas but have later disappeared, like the Moselle Romance and the Austrian Romance.

While the areas that now speak Friulian were originally inhabited by speakers of Venetic (likely Italic) and Celtic languages, the areas of Northeastern Italy that now speak Ladin initially spoke a non-Indo-European language called Raetic. Ladin and Romansh originate from the Vulgar Latin spoken by Roman soldiers during the conquests of Raetia.