This dissertation examines multiple exponence (ME) phenomena in the non-inflectional morphology of three languages: Nuu-chah-nulth (Wakashan), Central Yup'ik (Eskimo), and Korean (language isolate or Altaic). These languages exhibit a common property: ME comprised of a non-inflectional suffix and one or more base modifications. The base modifications involve a vowel length change and reduplication in Nuu-chah-nulth, various types of deletion in Central Yup’ik, and vowel shortening in Korean. This dissertation pursues four research questions: (1) what criteria diagnose morphophonological alternations as ME and do the criteria apply to all cases of ME to the same degree? (2) Does derivational ME differ from inflectional ME? (3) Does one exponent play a more significant role in expressing semantic/syntactic information than another? (4) How is derivational ME formally accounted for? In pursuit of these research questions, this study proposes, based on Matthews’s (1972) study, four criteria to distinguish ME from other phonological alternations. Only the two criteria, Non-phonological condition and Consistent co-occurrence are obligatory; two others, Phonological Consistency and No exceptions on base selection, may be violated, suggesting that ME parameters occur along a continuum. This dissertation also proposes derivational classes according to patterns of base modification. Derivational classes play an important role in formulating Word Formation Rules (WFRs), in that they provide the morphological conditions for the structural description of base modification rules. Significantly, semantic/syntactic information is encoded in suffixation, capturing the fact that the large number of meanings that suffixes carry (approximately 500) cannot be mapped onto a limited number of base modifications (ranging from two to fourteen). The evidence that suffixes convey meaning supports the claim that ME requires two different types of WFR, a suffixation rule that conveys semantic/syntactic information, and base modification rules that do not. Also, this study suggests that suffixes are the main exponent of ME because they make the main contribution to the meanings conveyed through ME. This study contributes to a theory of morphology not only in that seemingly distinct processes receive a unified analysis as ME, but also in that the distinct processes are formally accounted for, expanding the WP approach to derivational morphology. / Graduate / 0290 / sung17hwa@gmail.com