Declared the year of YouTube, 2007 was hailed as bringing a technological revolution in relation to pedagogy, one that may provide more convenient access to materials for language input, such as auditory, visual, and other types of authentic resources in order to promote advancement in all four language learning skills--listening, speaking, reading, and writing. Among these skills, for EFL or ESL students, listening comprehension provides the key opening access to language acquisition. This study examined and analyzed the effects of YouTube video clips as teaching material for EFL Taiwanese students on their listening comprehension performance. In more detail, it compared effects of employment of varied numbers of YouTube clips in three experimental groups with those found in a control group where no clips were used. Specific numbers of YouTube video clips--two, four, or six--used for each group represented an attempt to discover how many optimized results. A third purpose was to ascertain participant attitudes toward YouTube video clip use in listening activities. The subjects, 195 EFL college freshmen in a school located in Taichung, Taiwan, participated in a fourteen-week experimental research. Pre- and post tests and background survey were utilized for both control (0-video clip) and experimental groups (2-video, 4-video, and 6-video clips). The three experimental groups also answered an attitude questionnaire relating to YouTube video listening/viewing activities in week fourteen. Three notable results emerged. Foremost, YouTube listening/viewing activity presented statistically significant effects on subjects' listening comprehension performance. Next, the number of clips used in each group (0, 2, 4 and 6) successfully predicted the group differences found in the comparison of pre- and post test listening comprehension scores. In other words, the four varied numbers of YouTube clips used affected Taiwanese EFL students' achievement differently. The third finding showed that the three experimental groups exhibited little difference in attitudes based on the differing number of YouTube video clips used. However, an additional finding indicated that the attitude toward English learning in general had a significant positive effect in relation to listening achievement. These positive results imply that use of YouTube video clips provides an authentic native speaker setting that may be beneficial to EFL learners. Careful selection of such materials can enhance learner understanding of heard content. [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.]