Recent advances in mobile technologies have prompted their investigation as tools for language learning. Mobile-assisted language learning (MALL) offers the advantage of flexible language support, enabling learners to choose when and where they learn and the methods that suit them. The constant connectivity of modern mobile phones allows learners to access information and connect with resources almost anywhere and at any time. This study was designed to explore the ways in which adult international students in Japan use their mobile phones to support the acquisition of the native language (i.e., Japanese). Using data collected from interviews, the resulting qualitative analysis revealed the types of apps learners used to support their individual and social learning and how they used them, the benefits and challenges of MALL, perceived impact on learning, and recommendations for the improvement of mobile phones and apps. The results of this research are intended to offer learners insights to better support their own learning and provide instructors with information that can help improve course planning and instructional design. Further, this study hopes to provide device, peripheral, and application developers with data that may inform the production and development of more useful devices, tools, and educational software. [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.]