The Wu (吳方言 pinyin wu fang yan; 吳語 pinyin wu yu) spoken variations of the Chinese language are spoken in the provinces of Jiangsu and Zhejiang; and the municipality of Shanghai. Wu includes Shanghainese, Suzhou, Wenzhou, Hangzhou, Yongkang and Shaoxing dialects. As of 1991, there are 87 million speakers of Wu Chinese, making it the second largest form of Chinese after Mandarin Chinese (which has 800 million speakers).

Like all other varieties of Chinese, there is plenty of dispute as to whether Wu is a language or a dialect. Please see here for the issues surrounding this dispute.

Wu dialects are notable among Chinese languages in having kept voiced consonants, such as /b/, /d/, /g/, /z/, /v/, etc. (These may in fact be better described as voiceless consonants that create a voiced breathy element across the syllable: i.e. /p\/, /t\/, etc). Neither Mandarin nor Cantonese have voiced consonants. Differences in grammar also exist. Wu dialects have a relatively higher amount of Subject-Object-Verb sentence structure than Mandarin or Cantonese. There is huge array of personal and demonstrative pronouns used within the Wu dialects. Sandhi is also extremely complex, and helps parse multisyllabic words and idiomatic phrases. In some cases, indirect objects are distinguished from direct objects by a voiced/voiceless distinction.

It is thought that there are two branches of the Wu family of dialects, northern (Jiangsu), and southern (Zhejiang), with the southern dialects often being more conservative, tonally.

Jerry Norman general introduction to the Chinese language and dialects, Chinese (ISBN 0521228093), states that northern Wu dialects are much influenced in their phonology and vocabulary from the Mandarin dialects to the north. After the Japanese occupation of northern China during the Second World War, Japanese vocabulary entered Chinese which filtered down into Wu speaking areas.

The Japanese Go-on (呉音) pronunciation of Chinese characters (obtained from the Wu Kingdom during the Three Kingdoms period) is from the same region of China where Wu is spoken today.

See language tree of the Chinese dialects starting from 1500 BC, and Wu's position relative to them.