| Quốc ngữ translates literally as 'national language'. It is based on the standard dialect of the capital city Hanoi. Alexandre de Rhodes, its codifier in 1651, based his work on earlier research by Gaspar de Amaral and Antoine de Barbosa. It began as a text for transcribing Vietnamese in religious writings and spread to more general use because of its ease of learning in comparison with the less accurate Chữ nôm and Chữ nho systems. Official use began in 1910 with a decree from the ruling French colonial government requiring all public documents to be transcribed in Quốc ngữ. It has been developed by more modern scholars of the language, especially during the partition era from 1954 to 1975. In its current form its initial consonant portions most closely reflect south Vietnamese dialects, while final consonants are closer to those of north Vietnamese dialects. It is, however, an almost entirely phonetic script beyond these small inconsistancies.
There are thirty-seven letters/diagraphs of the language. They go as follows (with approximate equivalents for the consonants):
a; ă; â; b; c (k); ch; d (implosive d); đ (d); e; ê; g (velar fricative); gi (zh); h; i; k; kh (ch in loch); l; m; n; ng; nh (palatal n); o; ô; ơ; p; ph (f); q (k); r; s (sh); t; th (aspirated t); tr (retroflexive t); u; ư; v; x; y
Redundant consonants codifying the the same sound are used to distinguish the vowel quality of the sound they precede. K comes before a front vowel, while C comes before all other vowels and Q before the W morpheme (same as in Latinate languages, it's easy to see the influence of completely unrelated Romance languages on Vietnamese orthography).
Vietnamese word units are composed of an initial consonant (which may be empty in the case of a word beginning with a vowel), a vocalic nucleus, and an optional final consonant. The maximum length this can be expanded to is two syllables separated by a semivowel, otherwise the majority of Vietnamese words are one syllable. There are six individual tones. The level tone is left unmarked, the high rising tone is marked by an acute, the low falling is marked by an ague, the dipping-rising is marked by a strange diacritic hook resembling a Greek breathing mark (as in mả, 'tomb'), the high rising glottalized is marked by a tilde, and the low glottalized is marked by a dot (as in mạ, 'rice seedling'). These diacritics can be combined with ones already present to distinguish vowel quality.
Daniels, Peter T., Birhgt, William. The World's Writing Systems. Oxford University Press: Oxford, 1996. | 
