This study examined the effects of three subtitle conditions on English vocabulary learning, form recognition and meaning recall, from TED Talks videos while controlling for vocabulary size and initial knowledge of the target words. The participants, 105 Libyan students (16 males and 89 females) at intermediate English proficiency level, were assigned randomly to one of three groups. Group A, the control group, watched the TED Talks videos without subtitles. Group B watched the TED Talks videos with subtitles in English (L2). Group C watched the videos with Arabic (L1) subtitles. Data were collected from two pre-tests and two post-tests. Vocabulary Level Test (VLT) was used to measure learners' vocabulary size and served as a co-variate. Form Recognition (FR) and Meaning Recall (MR) tests were used to measure learners' depth of vocabulary knowledge at pre and post-tests. Analysis of covariance (ANCOVA) was used to respond to the study's research questions. The results indicated that there was no significant difference among the three groups' scores on either the FR or MR post-tests, controlling for vocabulary size and initial knowledge of the target words. Future studies with larger samples and multiple L2 and L1 subtitled video viewings (or other instructional supports that may be needed to support intermediate proficiency learners) are needed to more thoroughly examine subtitle effects on incidental vocabulary learning while controlling for relevant variables. [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.]