This dissertation has a couple of purposes: (1) to examine what writing knowledge and digital experiences are transferred/fail to be transferred to digital writing in a first-year writing class, and (2) to explore how writing knowledge, digital literacy, and students' prior writing experiences impact students' transfer between different activity systems. To address this study's research questions, multiple sets of data were employed: screencast videos of students' writing processes, students' writing samples, students' reflective journals, survey responses, and post-task stimulated recall interviews. Participants (n=8) were from a first-year composition class. Data were analyzed and categorized to achieve the above research purposes. The results of this study indicate that six knowledge domains are central to transfer when students wrote across different activity systems, including Anne Beaufort's (2007) Five Knowledge Domains (genre knowledge, discourse community knowledge, rhetorical knowledge, writing process knowledge, and subject knowledge) and digital literacy (functional, cognitive, critical, and rhetorical digital literacy skills). The skills, strategies, and knowledge that were transferred to college digital writing were from students' prior academic and non-academic (both digital and traditional) writing experiences. These strategies and knowledge were also tools for students to achieve their writing objectives within various activity systems. This study shows that the most salient tools that were transferred are "rhetorical digital literacy, cognitive digital literacy, functional digital literacy, genre knowledge, rhetorical knowledge," and "writing process knowledge." The findings also indicate that students' writing transfer was affected by the complex dynamics within and among activity systems, which resulted in six types of transfer practices: "dynamic, developmental, transformative, cross-contextual, rhetorical," and "idiosyncratic" transfer. Three types of transfer practices, "developmental, idiosyncratic," and "transformative" transfer, were found to be particularly significant in the study. On the one hand, students' writing transfer was mediated by external factors, notably through their interactions with genre conventions, discourse community conventions, and audience's expectations. On the other hand, it was also mediated by writers' agency, internal cognitive processes, and their unique personal experiences and knowledge bases. Therefore, when writing within an activity system, students learned about dominant genre conventions and discourse community knowledge, using them to guide their writing activities. In this way, students deepened and developed their understanding of those writing strategies and conventions and transferred them to new writing practices. That is, the "developmental transfer" occurred. In the meantime, they brought in their prior experiences, cultural and social stances, knowledge bases, or conventions from other communities or activity systems where they were simultaneously engaged in. In this sense, "idiosyncratic" and "transformative transfer" occurred. In brief, the interactions with different activity systems and writer's agency resulted in the occurrence of "developmental, idiosyncratic," and "transformative transfer." The findings of this study contribute significantly to the field of writing studies. Firstly, the study expands upon Beaufort's (2007) Five Knowledge Domain framework by incorporating "digital literacy" as the sixth domain. Secondly, it extends DePalma and Ringer's (2011) adaptive transfer framework by including a new category, "developmental transfer," and offering empirical evidence for all categories. Thirdly, the study proposes two new approaches to researching transfer. Lastly, it suggests using the Cultural Historical Activity Theory (CHAT) perspective to research and teach transfer. Based on the theoretical insights and empirical evidence presented in this study, two pedagogical recommendations are suggested: (1) teaching "digital literacy" to facilitate digital writing transfer, and (2) using multiple-activity-system-assignment sequence to promote transferability. [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.]