The Shanghainese language, also known as the Shanghai dialect, or Hu language, is a variety of Wu Chinese spoken in the central districts of the city of Shanghai and its surrounding areas. It is classified as part of the Sino-Tibetan language family. Shanghainese, like the rest of the Wu language group, is mutually unintelligible with other varieties of Chinese, such as Mandarin.

Shanghainese belongs to a separate group of the Taihu Wu subgroup. With nearly 14 million speakers, Shanghainese is also the largest single form of Wu Chinese. Since the late 19th century, it has served as the lingua franca of the entire Yangtze River Delta region, but in recent decades its status has declined relative to Mandarin, which most Shanghainese speakers can also speak.

Like other Wu varieties, Shanghainese is rich in vowels and consonants, with around twenty unique vowel qualities, twelve of which are phonemic. Similarly, Shanghainese also has voiced obstruent initials, which is rare outside of Wu and Xiang varieties. Shanghainese also has a low number of tones compared to other languages in Southern China and has a system of tone sandhi similar to Japanese pitch accent.

The speech of Shanghai had long been influenced by those dialects spoken about Jiaxing and Suzhou. Suzhounese literature, Chuanqi, Tanci, and folk songs all influenced early Shanghainese.

During the 1850s, the port of Shanghai was opened, and a large number of migrants, particularly from Ningbo and the Jianghuai area, entered the city. Around this time, missionaries such as Joseph Edkins and Tarleton Perry Crawford would document the phonology of the language. This led to many loanwords from both the West and the East, especially from Ningbonese, and like Cantonese in Hong Kong, English. In fact, "speakers of other Wu dialects traditionally treat the Shanghai vernacular somewhat contemptuously as a mixture of Suzhou and Ningbo dialects." This has led to Shanghainese becoming one of the fastest-developing languages of the Wu Chinese subgroup, undergoing rapid changes and quickly replacing Suzhounese as the prestige dialect of the Yangtze River Delta region. It underwent sustained growth that reached a peak in the 1930s during the Republican era, when migrants arrived in Shanghai and immersed themselves in the local tongue. Migrants from Shanghai also brought Shanghainese to many overseas Chinese communities. As of 2016, 83,400 people in Hong Kong are still able to speak Shanghainese. Shanghainese is sometimes viewed as a tool to discriminate against immigrants. Migrants who move from other Chinese cities to Shanghai have little ability to speak Shanghainese. Among the migrant people, some believe Shanghainese represents the superiority of native Shanghainese people. Some also believe that native residents intentionally speak Shanghainese in some places to discriminate against the immigrant population to transfer their anger to migrant workers, who take over their homeland and take advantage of housing, education, medical, and job resources.

After the People's Republic of China's government imposed and promoted Standard Chinese as the official language of all of China, Shanghainese had started its decline. During the Chinese economic reform of 1978, Shanghai has once again took in a large number of migrants. Due to the prominence of Standard Mandarin, learning Shanghainese was no longer necessary for migrants. However, Shanghainese remained a vital part of the city's culture and retained its prestige status within the local population. In the 1990s, it was still common for local radio and television broadcasts to be in Shanghainese. For example, in 1995, the TV series Sinful Debt featured extensive Shanghainese dialogue; when it was broadcast outside Shanghai (mainly in adjacent Wu-speaking areas) Mandarin subtitles were added. The Shanghainese TV series Lao Niang Jiu (老娘舅, "Old Uncle") was broadcast from 1995 to 2007; it was popular among Shanghainese residents. Shanghainese programming has since slowly declined amid regionalist-localist accusations. From 1992 onward, Shanghainese use was discouraged in schools, and many children native to Shanghai can no longer speak Shanghainese. In addition, Shanghai's emergence as a cosmopolitan global city consolidated the status of Mandarin as the standard language of business and services, at the expense of the local language.

Since 2005, movements to protect Shanghainese have emerged. At municipal legislative discussions in 2005, former Shanghai opera actress Ma Lili moved to "protect" the language, stating that she was one of the few remaining Shanghai opera actresses who still retained authentic classic Shanghainese pronunciation in their performances. Shanghai's former party boss Chen Liangyu, a native Shanghainese himself, reportedly supported her proposal. Shanghainese has been reintegrated into pre-kindergarten education, with education of native folk songs and rhymes, as well as a Shanghainese-only day on Fridays in the Modern Baby Kindergarten. Professor Qian Nairong, linguist and head of the Chinese Department at Shanghai University, is working on efforts to save the language. In response to criticism, Qian reminds people that Shanghainese was once fashionable, saying, "the popularization of Mandarin doesn't equal the ban of dialects. It doesn't make Mandarin a more civilized language either. Promoting dialects is not a narrow-minded localism, as it has been labeled by some netizens". Qian has also urged for Shanghainese to be taught in other sectors of education, due to kindergarten and university courses being insufficient.

During the 2010s, many achievements have been made to preserve Shanghainese. In 2011, Hu Baotan wrote Longtang (弄堂, "Longtang"), the first ever Shanghainese novel. In June 2012, a new television program airing in Shanghainese was created. In 2013, buses in Shanghai started using Shanghainese broadcasts. In 2017, Apple's iOS 11 introduced Siri in Shanghainese, being only the third Sinitic language to be supported, after Standard Mandarin and Cantonese. In 2018, the Japanese-Chinese animated anthology drama film Flavors of Youth had a section set in Shanghai, with significant Shanghainese dialogue. In January 2019, singer Lin Bao released the first Shanghainese pop record Shanghai Yao (上海謠, "Shanghai Ballad"). In December 2021, the Shanghainese-language romantic comedy movie Myth of Love (愛情神話) was released. Its box office revenue was ¥260 million, and response was generally positive. Similarly, in December 2023, the TV show Blossoms Shanghai (繁花) aired with the primary language being Shanghainese.