This article draws upon Bergmann and Zepernick's (2007) metaphor of the box under the bed to investigate the relationship between students' epistemologies and their learning transfer in diverse contexts over undergraduate years. We present a systemic analysis of 13 students' interviews and writing samples over a five-year period, through which we explored students' transfer-related epistemologies surrounding writing in diverse disciplines. We describe three primary types of students' epistemologies, the factors that influence the development of these transfer-based epistemologies, and the relationship between students' epistemologies and reported learning transfer and genre knowledge. This article concludes by discussing how understanding students' learner epistemologies can improve pedagogical practices that help students engage with prior writing knowledge in disciplinary writing contexts and suggests new directions for transfer theory and research.