The current dissertation investigated segmental and prosodic aspects of first- (L1) and second-language (L2) speech production. Forty Korean-speaking adults and children varying in L2 experience (6 months-inexperienced vs. 6 years-experienced) as well as twenty age-matched native English speaking adults and children participated. Experienced children born in the U.S. were first exposed to English much earlier than inexperienced children. Group differences were investigated for insight into the effect of differing language experience on speech production. For segmental aspects, spectral quality and duration of English and Korean vowels (Chapter II), the effect of English coda consonant voicing on vowel and consonant closure duration (Chapter III), and language-specific voice onset time (VOT) in English and Korean stops (Chapter IV) were examined. All Korean groups except the experienced children differed from the native English speakers in vowel spectral quality and coda voicing production. The experienced children showed native-like production of both English and Korean vowels and also used VOT to distinguish Korean aspirated and English voiceless stops. These results suggest that the experienced children have separate phonological representations for their two languages. For prosodic aspects, stressed and unstressed vowels in English multisyllabic words (Chapter V) and Korean four-syllable phrases (Chapter VI) were elicited. The results of stressed and unstressed vowel production revealed that the Korean adults were able to acquire English prosody in a native-like manner, except for reduced vowel quality. Contrary to the little L1-L2 interaction in prosody for adults, Korean experienced children's production suggested a strong influence of English acquisition on the development of Korean prosody in terms of fundamental frequency, intensity, and duration patterns. Different degrees of L1-L2 interaction between Korean experienced children's production of segments and prosody are discussed from the developmental standpoint of simultaneous bilingual children's language shift from the mother tongue to English. In addition to children's greater plasticity of language acquisition, external (e.g., peer pressure, language input) and internal (e.g., ethnic self-identity) factors are likely to have created a language learning environment different from that of the Korean adults. As a result, the degree and direction of L1-L2 interaction varied by linguistic domains, depending on the age of the learner and the language experience. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]