The Ryukyuan languages (琉球語派, Ryūkyū-goha; also 琉球諸語, Ryūkyū-shogo or 島言葉 in Ryukyuan, Shima kotoba, literally "Island Speech"), also Lewchewan or Luchuan (/luːˈtʃuːən/), are the indigenous languages of the Ryukyu Islands, the southernmost part of the Japanese archipelago. Along with the Japanese language and the Hachijō language, they make up the Japonic language family.

Just as among Japanese dialects, which can have low mutual intelligibility, the Ryukyuan and mainland Japanese languages are not mutually intelligible. It is not known how many speakers of these languages remain, but language shift toward the use of Standard Japanese and dialects like Okinawan Japanese has resulted in these languages becoming endangered; UNESCO labels four of the languages "definitely endangered" and two others "severely endangered".

Phonologically, the Ryukyuan languages have some cross-linguistically unusual features. Southern Ryukyuan languages have a number of syllabic consonants, including unvoiced syllabic fricatives (e.g. Ōgami Miyako /kss/ [ksː] 'breast'). Glottalized consonants are common (e.g. Yuwan Amami /ʔma/ [ˀma] "horse"). Some Ryukyuan languages have a central close vowel rather than the more common front and back close vowels [i] and [u], e.g. Yuwan Amami /kɨɨ/ "tree". Ikema Miyako has a voiceless nasal phoneme /n̥/. Many Ryukyuan languages, like Standard Japanese and most Japanese dialects, have contrastive pitch accent.

Ryukyuan languages are generally subject–object–verb (SOV) order, dependent-marking, modifier-head, nominative-accusative languages, like Japanese. Adjectives are generally bound morphemes, occurring either with noun compounding or using verbalization. Many Ryukyuan languages mark both nominatives and genitives with the same marker. This marker has the unusual feature of changing form depending on an animacy hierarchy. The Ryukyuan languages have topic and focus markers, which may take different forms depending on the sentential context. Ryukyuan also preserves a special verbal inflection for clauses with focus markers—this unusual feature was also found in Old Japanese, but lost in Modern Japanese.

The Ryukyuan languages belong to the Japonic language family, related to the Japanese language. The Ryukyuan languages are not mutually intelligible with Japanese—indeed, Ryukyuan languages are largely not mutually intelligible with each other—and thus are usually considered separate languages. However, for socio-political and ideological reasons, they have often been classified within Japan as dialects of Japanese. Since the beginning of World War II, most mainland Japanese have regarded the Ryukyuan languages as a dialect or group of dialects of Japanese.

The Okinawan language is only 71% lexically similar to, or cognate with, standard Japanese. Even the southernmost Japanese dialect (Kagoshima dialect) is only 72% cognate with the northernmost Ryukyuan language (Amami). The Kagoshima dialect of Japanese, however, is 80% lexically similar to Standard Japanese. There is general agreement among linguistics experts that Ryukyuan varieties can be divided into six languages, conservatively, with dialects unique to islands within each group also sometimes considered languages.

A widely accepted hypothesis among linguists categorizes the Ryukyuan languages into two groups, Northern Ryukyuan (Amami–Okinawa) and Southern Ryukyuan (Miyako–Yaeyama). Many speakers of the Amami, Miyako, Yaeyama and Yonaguni languages may also be familiar with Okinawan since Okinawan has the most speakers and once acted as the regional standard. Speakers of Yonaguni are also likely to know the Yaeyama language due to its proximity. Since Amami, Miyako, Yaeyama, and Yonaguni are less urbanized than the Okinawan mainland, their languages are not declining as quickly as that of Okinawa proper, and some children continue to be brought up in these languages.^{[citation needed]}

Each Ryukyuan language is generally unintelligible to others in the same family. There is wide diversity among them. For example, Yonaguni has only three vowels, whereas varieties of Amami may have up to seven, excluding length distinctions. The table below illustrates the different phrases used in each language for "thank you" and "welcome", with standard Japanese provided for comparison.