Modern Standard Hindi is the official language of India, while Urdu is the national language of Pakistan as well as a scheduled language in India. The two are often held as separate languages on the bases of higher vocabulary choice (and thus mutual intelligibility) as well as cultural orientation (see Ausbau); however on a linguistic basis they are two standardized registers of a single subdialect, that being the Khari boli dialect of Delhi (a pluricentric language). In keeping with such a linguistic analysis, Hindi and Urdu occupy a single descriptive phonology page, with attention paid to phonological variations between the two registers, and associated dialects, wherever they arise.

Hindi/Urdu natively possesses a symmetrical ten-vowel system. The vowels: [ə], [ɪ], [ʊ] are always short in length, while the vowels: [aː, iː, uː, eː, oː, ɛː, ɔː] are always considered long (but see the details below). Among the close vowels, what in Sanskrit are thought to have been primarily distinctions of vowel length (that is /i ~ iː/ and /u ~ uː/) have become in Hindi/Urdu distinctions of quality, or length accompanied by quality (that is, /ɪ ~ iː/ and /ʊ ~ uː/). The historical opposition of length in the close vowels has been neutralized in word-final position, for example Sanskrit loans śakti (शक्ति– شکتی 'energy') and vastu (वस्तु – وستو 'item') are /ʃəkt̪i/ and /ʋəst̪u/, not */ʃəkt̪ɪ/ and */ʋəst̪ʊ/.