Theoretical background for researching student learning, engagement, and collaboration through the development of electronic portfolios is described in this article. After providing an overview of the limited research on portfolios in education, the author discusses the accepted definitions, multiple purposes, and conflicting theoretical paradigms of electronic portfolios. Principles of student motivation and engagement are covered, and the philosophical issues related to portfolio assessment and reflection are outlined--paying particular attention to the difference between assessment "for" learning and assessment "of" learning. Finally, the article describes how the REFLECT Initiative will begin to fill the current void in empirical data on electronic portfolio implementation at the secondary level. (Contains 2 tables.)