Japanese (日本語, Nihongo, [ɲihoŋɡo] (listen)) is spoken as a native language by about 128 million people, primarily Japanese people and primarily in Japan, the only country where it is the national language. Japanese belongs to the Japonic or Japanese-Ryukyuan language family. There have been many attempts to group the Japonic languages with other families such as the Ainu, Austroasiatic, Koreanic, and the now-discredited Altaic, but none of these proposals has gained widespread acceptance.

Little is known of the language's prehistory, or when it first appeared in Japan. Chinese documents from the 3rd century AD recorded a few Japanese words, but substantial Old Japanese texts did not appear until the 8th century. From the Heian period (794–1185), extensive waves of Sino-Japanese vocabulary entered the language, affecting the phonology of Early Middle Japanese. Late Middle Japanese (1185–1600) saw extensive grammatical changes and the first appearance of European loanwords. The basis of the standard dialect moved from the Kansai region to the Edo region (modern Tokyo) in the Early Modern Japanese period (early 17th century–mid 19th century). Following the end of Japan's self-imposed isolation in 1853, the flow of loanwords from European languages increased significantly, and words from English roots have proliferated.

Japanese is an agglutinative, mora-timed language with relatively simple phonotactics, a pure vowel system, phonemic vowel and consonant length, and a lexically significant pitch-accent. Word order is normally subject–object–verb with particles marking the grammatical function of words, and sentence structure is topic–comment. Sentence-final particles are used to add emotional or emphatic impact, or form questions. Nouns have no grammatical number or gender, and there are no articles. Verbs are conjugated, primarily for tense and voice, but not person. Japanese adjectives are also conjugated. Japanese has a complex system of honorifics, with verb forms and vocabulary to indicate the relative status of the speaker, the listener, and persons mentioned.

The Japanese writing system combines Chinese characters, known as kanji (漢字, 'Han characters'), with two unique syllabaries (or moraic scripts) derived by the Japanese from the more complex Chinese characters: hiragana (ひらがな or 平仮名, 'simple characters') and katakana (カタカナ or 片仮名, 'partial characters'). Latin script (rōmaji ローマ字) is also used in a limited fashion (such as for imported acronyms) in Japanese writing. The numeral system uses mostly Arabic numerals, but also traditional Chinese numerals.