The Japanese language is written in a mixture of three scripts; kanji, which is derived from Chinese characters and represents logographic or morphological units, and two kana, pairs of syllabaries. The two kana are called hiragana and katakana. A single text usually contains all three scripts. Kanji is used for writing nouns, verb stems, adjective stems and some adverbs. Hiragana is used primarily for grammatical elements - particles, inflectional endings and auxiliary verbs. Katakana is used for writing loan words, onomatopoeic words, to give emphasis, to suggest a conversational tone, or to indicate irony or a euphemism. The two kana can also be used to write a word for which the writer does not know the kanji character. A fourth writing system, Roman, is also used in small amounts, particularly for writing numerals. The Japanese writing system is neither syllabic nor logographic, but uses elements of both in tandem.

Kanji characters were introduced to Japan around the 3rd century, it is thought from Korea. Until the 7th or 8th century, the Japanese language was written exclusively in these Chinese characters. Initially these were used phonetically to represent similar-sounding Japanese syllables, regardless of their meaning in written Chinese. However, the process of writing Japanese solely in kanji was laborious; each symbol consisted of a number of strokes and only represented one syllable. Two simplified forms of writing began to emerge around the 7th century. The modern hiragana script developed from a simplified cursive style originally developed by women, who were discouraged from learning kanji, and katakana was developed by Buddhist scholars who wrote only one element of each kanji symbol as a form of shorthand.

In modern written Japanese, many kanji characters can be read in two ways. On-readings are based on the Chinese pronunciation of the character at the time of borrowing, irrespective of any subsequent changes in meaning, while kun-readings are based on the pronunciation of the Japanese word having the same meaning. For example, the loan word nin is based on the sound of the Mandarin word rén 'person', which is written with the character 人. The native Japanese word having the same meaning - 'person' - is pronounced hito. So the character 人 can be pronounced either nin (the on-reading), or hito (the kun-reading). To avoid confusion, small-type kana are sometimes written alongside or above a kanji character to indicate which pronunciation is intended.

Spoken Japanese contains a large number of homophones - words which are pronounced the same but have different meanings. To avoid ambiguity, different kanji can be used to indicate which meaning is intended. For example, the word for both 'science' and 'chemistry' is kagaku, but the former meaning is written using the symbols meaning 'division' + 'study', and the latter, the symbols meaning 'change' + 'study'. The ability to disambiguate in this way using kanji is one of the reasons often cited in opposition to proposals to eliminate kanji altogether and only use kana.