Hanyu Pinyin (simplified Chinese: 汉语拼音; traditional Chinese: 漢語拼音; pinyin: hànyǔ pīnyīn), often shortened to just pinyin, is the foremost romanization system for Standard Mandarin Chinese. It is used in either a formal, educational or official capacity in countries where the language is official, which are the People's Republic of China (PRC), the Republic of China (ROC, Taiwan) and Singapore, as well as in the United Nations (UN). It is principally used to teach Mandarin, normally written with Chinese characters, to learners already familiar with the Latin alphabet. The system includes four diacritics denoting tones, but pinyin without tone marks is used to spell Chinese names and words in languages written in the Latin script, and is also used in certain computer input methods to enter Chinese characters. The word Hànyǔ (simplified Chinese: 汉语; traditional Chinese: 漢語) literally means "Han language" (i.e. Chinese language), while Pīnyīn (拼音) means "spelled sounds".

The pinyin system was developed in the 1950s by a group of Chinese linguists including Zhou Youguang and was based on earlier forms of romanizations of Chinese. It was published by the Chinese Government in 1958 and revised several times. The International Organization for Standardization (ISO) adopted pinyin as an international standard, ISO 7098, in 1982 and was followed by the United Nations in 1986. Attempts to make pinyin standard in the ROC (Taiwan) occurred in 2002 and 2009, and while official since 2009, "Taiwan largely has no standardized spelling system" so that in 2019 "alphabetic spellings in Taiwan are marked more by a lack of system than the presence of one". Moreover, "some cities, businesses, and organizations, notably in the southern parts of Taiwan, did not accept [efforts to introduce pinyin] due to political reasons, as it suggested further integration with the PRC", and so it remains one of several rival romanization systems in use.

When a foreign writing system with one set of coding and decoding systems is taken to write a language, certain compromises may have to be made. The result is that the decoding systems used in some foreign languages will enable non-native speakers to produce sounds more closely resembling the target language than will the coding and decoding systems used by other foreign languages. Native speakers of English will decode pinyin spellings to fairly close approximations of Mandarin except in the case of certain speech sounds that are not ordinarily produced by most native speakers of English: j /tɕ/, q /tɕʰ/, x /ɕ/, z /ts/, c /tsʰ/, zh /ʈʂ/, ch /ʈʂʰ/, h /x/ and r /ɻ/ exhibit the greatest discrepancies.

In this system, the correspondence between the Latin letters and the sound is sometimes idiosyncratic, though not necessarily more so than the way the Latin script is employed in other languages. For example, the aspiration distinction between b, d, g and p, t, k is similar to that of these syllable-initial consonants in English (in which the two sets are, however, also differentiated by voicing), but not to that of French. Letters z and c also have that distinction, pronounced as [ts] and [tsʰ] (which is reminiscent of these letters being used to represent the phoneme /ts/ in the German language and Slavic languages written in the Latin script, respectively). From s, z, c come the digraphs sh, zh, ch by analogy with English sh, ch. Although this analogical use of digraphs introduces the novel combination zh, it is internally consistent in how the two series are related. In the x, j, q series, the pinyin use of x is similar to its use in Portuguese, Galician, Catalan, Basque, and Maltese to represent /ʃ/; the pinyin q is close to its value of /c͡ç/ in Albanian, though to the untrained ear both pinyin and Albanian pronunciations may sound similar to the ch. Pinyin vowels are pronounced in a similar way to vowels in Romance languages.

The pronunciations and spellings of Chinese words are generally given in terms of initials and finals, which represent the language's segmental phonemic portion, rather than letter by letter. Initials are initial consonants, whereas finals are all possible combinations of medials (semivowels coming before the vowel), a nucleus vowel, and coda (final vowel or consonant).