Cantonese is the traditional prestige variety of Yue Chinese, a Sinitic language belonging to the Sino-Tibetan language family. It originated in the city of Guangzhou (formerly romanized as Canton) and its surrounding Pearl River Delta. Although Cantonese specifically refers to the prestige variety in linguistics, the term is often used more broadly to describe the entire Yue subgroup of Chinese, including varieties such as Taishanese, which have limited mutual intelligibility with Cantonese.

Cantonese is viewed as a vital and inseparable part of the cultural identity for its native speakers across large swaths of southeastern China, Hong Kong, and Macau, as well as in overseas communities. In mainland China, it is the lingua franca of the province of Guangdong (being the majority language of the Pearl River Delta) and neighbouring areas such as Guangxi. It is also the dominant and co-official language of Hong Kong and Macau. Further, Cantonese is widely spoken among overseas Chinese in Southeast Asia (most notably in Vietnam and Malaysia, as well as in Singapore and Cambodia to a lesser extent) and the Western world. With about 80 million total speakers as of 2023, standard Cantonese is by far the most spoken variant of Yue Chinese and non-Mandarin Chinese language.

Although Cantonese shares much vocabulary with Mandarin and other varieties of Chinese, these Sinitic languages are not mutually intelligible, largely because of phonological differences, but also differences in grammar and vocabulary. Sentence structure, in particular the verb placement, sometimes differs between the two varieties. A notable difference between Cantonese and Mandarin is how the spoken word is written; both can be recorded verbatim, but very few Cantonese speakers are knowledgeable in the full Cantonese written vocabulary, so a non-verbatim formalized written form is adopted, which is more akin to the written Standard Mandarin. However, it is only non-verbatim with respect to vernacular Cantonese as it is possible to read Standard Chinese text verbatim in formal Cantonese, often with only slight changes in lexicon that are optional depending on the reader's choice of register. This results in a situation in which a Cantonese and a Mandarin text may look similar but are pronounced differently. Conversely, written (vernacular) Cantonese is mostly used in informal settings like social media and comic books.

In English, the term "Cantonese" can be ambiguous. "Cantonese" as used to refer to the language native to the city of Canton, which is the traditional English name of Guangzhou, was popularized by An English and Cantonese Pocket Dictionary (1859), a bestseller by the missionary John Chalmers. Before 1859, this variant was often referred to in English as "the Canton dialect".

However, "Cantonese" may also refer to the primary branch of Chinese that contains Cantonese proper as well as Taishanese and Gaoyang; this broader usage may be specified as "Yue speech" (粵語; 粤语; Jyut6 jyu5; Yuhtyúh). In this article, "Cantonese" is used for Cantonese proper (Guangzhou).

Historically, speakers called this variety "Guangzhou speech" (廣州話; 广州话; Gwong2 zau1 waa2; Gwóngjāu wá), although this term is now seldom used outside mainland China. In Guangdong and Guangxi, people also call it "provincial capital speech" (省城話; 省城话; Saang2 seng4 waa2; Sáangsèhng wá) or "plain speech" (白話; 白话; Baak6 waa2; Baahkwá). In academic linguistic circles, it is also referred to as "Guangzhou prefecture speech" (廣府話; 广府话; Gwong2 fu2 waa2; Gwóngfú wá).

In Hong Kong and Macau, as well as among overseas Chinese communities, the language is referred to as "Guangdong speech" or "Canton Province Speech" (廣東話; 广东话; Gwong2 dung1 waa2; Gwóngdūng wá) or simply as "Chinese" (中文; Zung1 man2; Jūngmán).

During the Southern Song period, Guangzhou became the cultural center of the region. Cantonese emerged as the prestige variety of Yue Chinese when the port city of Guangzhou on the Pearl River Delta became the largest port in China, with a trade network stretching as far as Arabia. Specifically, the mutually intelligible speech of the Sam Yap (三邑), the Three Counties of Guangzhou, namely the historical counties of Panyu (番禺), Nanhai (南海), and Shunde (顺德), came to be heralded as the standard. Cantonese was also used in the popular Yuè'ōu, Mùyú and Nányīn folksong genres, as well as Cantonese opera. Additionally, a distinct classical literature was developed in Cantonese, with Middle Chinese texts sounding more similar to modern Cantonese than other present-day Chinese varieties, including Mandarin.