With the increasing number of young emergent multilingual language learners in transnational contexts, there is a growing need to explore and examine how emergent multilingual children develop their translingual competence and how they exercise their agency to engage in translingual practices across different settings (e.g., home and school). Yet, a few studies on emergent multilingual children's translingual practices and their agency were conducted in the L2 writing field due to the difficulties of the actual enactment of translingual writing pedagogy. In response to this, this qualitative case study attempts to investigate how, to what extent, and on what purposes emergent multilingual children engage in translingual writing practices within and across three different contexts (school, home, and community) as well as in a translingual writing program, a specially designed afterschool program in school, and the relationship between their participation in translingual writing practices and exercising their agency. Drawing upon the theoretical frameworks of translingualism and agency from a social view, this study employs multiple sources of data to build a multifaceted perspective on three focal participants' translingual writing practices and the enactment of their agency in school, home, and community over the course of four months. The data include video recordings of the program meetings, observations, fieldnotes, interviews, documents, and artifacts (e.g., surveys, writings, and literacy logs). The findings from this dissertation suggest that these emergent multilinguals participated in a wide variety of translingual practices for different purposes within and across the three contexts. An important finding here is that their engagement in translingual practices became more agentive and active under the circumstances in which their multilingual beliefs and competence were valued, and where a relatively large number of resources were available to them. Also, although the learners often utilized varied languages in their writing practices and processes, their multiple language use was hardly observed in their final products (e.g., writing samples) for the program and school projects. The findings also show that learners' Korean language proficiency influenced their translingual practices, particularly in school, having an impact on their use of Russian in educational contexts. The analysis of the learners' participation in the translingual writing program reveals the three affordances of the program: (1) exploration and examination of linguistic and cultural differences, (2) noticing the likelihood of multiple language use for varied purposes, and (3) becoming more agentive in using placed resources. The three affordances indicate that the learners' translingual experiences and growing translingual competence in the program enhance their language awareness which enables them to exercise their agency to (re)organize social conditions and relationships for meaningful negotiation. In the program, the emergent multilinguals reshape their agency to participate in translingual writing practices according to their linguistic and cultural repertoire, available resources, their purposes, and language values embedded in contexts. It provides evidence to the relationship between their agency and translingual writing practices which highlights the importance of offering a translingual space to emergent multilingual language learners and contributes to the in-depth understanding of the implementation of translingual writing pedagogy. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]