The phonological origin of the modern-day Mandarin can be traced back to the fourteenth-century northern dialect. In this chapter, the discussion on the use of Putonghua and Cantonese in the Chinese territories, the former being the national common language, and the latter a particularly vitalized regional dialect spoken in the Pearl River Delta, including Hong Kong and Macao, shall start with a brief introduction of this phonological origin and the formation of the common language in China. This will be followed by information on its spread and use in the present day, and its interaction with the Cantonese dialect in the two above-named special administrative regions of China.