This project investigated second language writing teachers’ writing assessment literacy by looking at teachers’ practices of electronic writing portfolios (e-WPs), as well as the sources that shape L2 writing teachers’ knowledge of e-WPs in the context of multilingual First-Year Composition (FYC) classrooms. By drawing on Borg’s (2003) theory of teacher cognition and Crusan, Plakans, and Gebril’s (2016) definition of assessment literacy, I define L2 teachers’ writing assessment literacy as teachers’ knowledge, beliefs and practices of a particular assessment tool, affected by institutional factors. While teachers are the main practitioners who help students create e-WPs (Hilzensauer & Buchberger, 2009), studies on how teachers actually incorporate e-WPs in classes and what sources may influence teachers’ knowledge of e-WPs, are scant. To fill in this gap, I analyzed data from sixteen teachers’ semi-structured interviews. Course syllabi were also collected to triangulate the interview data. The interview results indicated that 37.5 % of the teachers use departmental e-WPs with the goal of guiding students throughout their writing process. 43.7 % of the teachers do not actively use e-WPs and have students upload their writing projects only to meet the writing program’s requirement at the end of the semester. The remaining 18.7 % use an alternative platform other than the departmental e-WP platform, throughout the semester. Sources influencing teachers’ e-WP knowledge included teachers’ educational and work experience, technical difficulties in the e-WP platform, writing program policies and student reactions. The analysis of the course syllabi confirmed the interview results. Based on the findings, I argue that situated in the context of classroom assessment, institutional factors plus teachers’ insufficient knowledge of e-WPs limit the way teachers communicate with students, whose reactions cause teachers to resist e-WPs. Conversely, teachers’ sufficient knowledge of e-WPs enables them to balance the pressure from the institutional factors, generating positive reactions from the students. Students’ positive reactions encourage teachers to accept the departmental e-WPs or use similar alternative e-WP platforms. Pedagogical implications, limitations of the study and suggestions for future research are reported to conclude the dissertation.