This design-based study of 20 adolescents and their teachers in the United States and South Korea examines how participants negotiate language and literacy practices in a digitally mediated transnational network. Drawing on New Literacy Studies (Gee, 2015; Street, 2003), this study seeks to broaden the concept of a transnational community to include a growing number of transnational individuals and communities accelerated by digital development and to cultivate global citizens through intercultural communication. In particular, this dissertation explores the language and literacy practices of Korean adolescents near or on borders by expanding the concepts of transnationalism and the transnational community to include an examination of multiple borders such as language, identity, nations, geography, and medium for literacy practices. Employing a design-based study (Barab & Squire, 2004), this dissertation focused on language and literacy mapping activities co-designed by the teachers, students and the researcher. Multiple data sources were collected over one academic year in two local classrooms and a global online community and analyzed inductively. The key finding that emerged from the analysis of the two groups of Korean adolescents’ language and literacy practices was that these students engaged in transnational practices not only by crossing but also by connecting multiple borders in multimodal composing landscapes. This study tells the interrelated stories of transnational language and literacy practices by which adolescents who have heightened awareness of borders engaged in a digitally mediated transnational space to share their lived experiences, communicate in multiple languages and modes, and collaborate across borders.