In this dissertation, I provide a new analysis of the Vietnamese vowel system as a system with fourteen monophthongs and nineteen diphthongs based on phonetic and phonological data. I propose that these Vietnamese contour vowels- /ie/, /ɯɤ / and /uo /- should be grouped with these eleven monophthongs /i e ɛ a ɐ ʌ ɤ ɯ u o ɔ / based on their similarities in phonetic and phonological behaviors. The phonetic characteristics of these vowels are studied acoustically using normalized and scaled acoustic values of 13,925 tokens, spoken by female Hanoian speakers from my speech corpus, "The Vietnamese Speech Corpus". Phonetic analysis shows that the eleven monophthongs and three contour vowels are similar in terms of formant frequency targ...