To provide multi-dimensional support for undergraduates from traditionally underrepresented backgrounds who aspire to careers in research, the BUILD EXITO project, part of a major NIH-funded diversity initiative, matches each scholar with three mentors: peer mentor (advanced student), career mentor (faculty adviser), and research mentor (research project supervisor). After describing the aims of the diversity initiative, the institutional context of the BUILD EXITO project, and the training program model, this article devotes special attention to the rationale for and implementation of the peer mentoring component within the context of the multi-faceted mentoring model.