The present study examined the effects of multimedia enhancement in video form in addition to textual information on L2 vocabulary instruction for high-level, low-frequency English words among Korean learners of English. Although input-based incidental learning of L2 vocabulary through extensive reading has been conventionally believed to be appropriate for high-frequency words, intentional or explicit vocabulary learning is suggested to be more sensible or realistic for the acquisition of low-frequency academic words. Multimedia support in foreign language instruction has revealed benefits in promoting direct teaching and explicit learning of L2 vocabulary; moreover, adding textual information to video seems to boost students' understanding of the learning materials. Under the theoretical frameworks such as the "dual-coding theory" and the "cognitive load theory," the study investigated (1) multimedia effects on vocabulary acquisition of advanced-level infrequent words, (2) the best way to offer multimedia by combining the optimal modes of presentation, and (3) the aspects in multimedia support that can help students with acquisition and retention of unfamiliar words. Seventy-four Korean students who were preparing for the GRE for graduate study in the U.S. participated in the experiment. They were randomly divided into four different groups and were given instruction on 34 GRE vocabulary words in four different conditions: Text-only, Text+Audio, Text+Video, or Text+Audio+Video. After each treatment, immediate post-tests and seven-day delayed post-tests were administered to evaluate participant score change from the pre-tests. Results indicate that multimedia presentation has a greater positive effect on learning than text-only presentation, supporting the "dual-coding theory." Among the types of multimedia support, Text+Audio+Video appears to be better than Text+Audio or Text+Video, suggesting the benefit of the combination of audio and video. Moreover, multimedia audio-visual support was found to be more advantageous when supplemented with a linguistic cue in the form of a precise definition or synonym of an unknown word. Findings have both theoretical and pedagogical implications in L2 vocabulary acquisition of high-level, low-frequency English words in that the study addressed ways to design effective multimedia materials and offered instructional guidelines for multimedia language teaching. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]