Writer identity has gradually become a focus in writing scholarship in recent years. From a social constructivist lens, writer identity is not optional; it resides in all texts. And it is a construct that does not exist in a vacuum, but is shaped by the sociocultural and academic context, and simultaneously individual writers agentively select from the socially available repertoire to construct their identities in text. Departing from social constructivism, this study adopted Ivanic's (1998) conceptualization of writer identity, which consists of "autobiographical self," "discoursal self," "self as author" and "possibilities for selfhood," and highlighted the role of agency in the construction of writer identity. This dissertation employed a multi-case study design, and looked into how three L2 doctoral students studying in the U.S. setting constructed their identities in their academic papers of different kinds and the patterns of identity construction across their papers. Among the three participants, two came from the hard discipline background whereas the other one from soft discipline. Further, this study examined the variables, including contextual factors ("autobiographical self" and "possibilities for selfhood") and individual agency, that contributed to the three L2 doctoral students' identity construction in their papers. Data collected for this study included three writing samples from each of the students, and three to four rounds of interviews with the participants. Interviews encompassed background interviews, and interviews about the papers. Supplementary data were also collected to provide additional insights into the students' identity construction that included research log, advisors'/reviewers'/co-authors' feedback on the papers, course syllabi and so on. This dissertation analyzed writer identity through combining Hyland's (2018) metadiscourse model and interactional model (2005). The findings revealed that the three strands of metadiscourse followed the same pattern in all the three students' papers, showing that these three students probably attached more importance to constructing identities as writers using explicit linguistic devices to glue texts together and to signal the internal relations of their text. Comparatively, they tended to project identities less prominently as writers who engaged readers directly in the texts. However, more metadiscourse markers were found in the doctoral student' papers from the soft discipline. This demonstrated the more discursively elaborate nature of the soft discipline, where writers may need more metadiscoursal items to construct their identities as disciplinary insiders. The findings further showed that the three participants' construction of identities through metadiscourse resources was shaped by contextual factors such as field conventions and senior researchers' guidance. Agency, however, played a relatively minor role in the construction of their identities in the academic papers. Insights generated from the study and directions for future research are discussed. [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.]