This dissertation examines whether EFL and ESL Korean learners of English are able to produce and perceive two English phonological contrasts that depend on vowel duration differences, coda consonant voicing contrasts and the tense-lax distinction in vowels. For production, it examines differences in vowel duration and vowel quality associated with both contrasts. Also, for the voicing contrast, it investigates whether Korean coda neutralization influences Korean speakers' performance by incorporating environments where neutralization occurs in Korean (in final, coda position) and where it does not occur (in medial, inter-vocalic position). For perception, it further examines these learners' abilities to perceptually identify and discriminate these same contrasts. Finally, it examines the relationship between production and perception of the two English contrasts by Korean speakers via cross-subject analysis. In production, all speakers exhibited durational correlates for both contrasts. However, both EFL and ESL Korean learners failed to produce the spectral cues effectively. In perception, all speakers were good at perceptually distinguishing English consonant voicing contrasts whereas they had more difficulty in perceptually differentiating English tense/lax vowel contrasts. Cross-subject analysis does not indicate a correlation between vowel length differences in production and perception scores and the different individuals have different production and perception processes in English language acquisition. EFL and ESL learners of Korean exhibited no systematic differences in skill in either production or perception, thus not indicating any effect of exposure to English in an English-speaking country. Altogether, these findings imply that the production and perception skills associated with each contrast are independent. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]