This study aims at constructing a fully articulated theory of tone-vowel interaction within the framework of Optimality Theory (OT). It examines the nature of this phenomenon in Northern Min languages, as well as various Southeast Asian languages. The questions addressed are (i) what is the nature of tone-vowel interaction? (ii) how do they relate to each other? Two important findings emerge from the investigation. First, tonal types and syllable types are closely related to each other. That is, different groups of tones occur only in a certain kind of syllables. These cooccurrence restrictions are identified as a correlation between tonal contour and syllable weight. Second, tone does not directly affect vowel distributions and alternations. Rather, it is the relative syllable positions in which a vowel occurs and the number of segments present in a syllable that trigger vowel distributions and alternations. These findings lead to the conclusion that tone and vowel do not interact directly and that there is no feature-to-feature correlation between them. Their interaction lies in the prosodic anchor mediating between them. To account for the correlation between tonal contour and syllable weight and the close relationship between syllable structures and vowel features, a prosodic anchor hypothesis is proposed which attributes the tone-vowel interaction to the mora and its function as an anchor for both tone and vowel.