Self-reported positive effects of peer mentoring for mentors and mentees have included enhanced academic performance, greater sense of belonging, and retention, among other widely accepted benefits of the intervention. However, minimal quantitative or mixed methods research has focused on mentoring staff who design, implement, and therefore heavily influence these programs. This mixed-methods study sought to articulate which factors relate to staff beliefs on peer mentoring in California's largest public higher education system, the California State University. The first purpose of this study was to articulate which facets relate to or contribute to beliefs on a spectrum of mentoring perspectives, from traditional to critical mentoring pedagogy. The second, related purpose was to design an instrument to measure the structure of critical mentoring beliefs with a sample of staff who work in CSU mentoring programs. Findings from psychometric analyses will inform the development of the Critical Mentoring Beliefs Scale (CMBS). The findings have implications for valid, reliable and unbiased measures of practitioner beliefs in the mentoring field, with recommendations for future research related to mentoring constructs and the instrumentation used to operationalize claims about beliefs, attitudes, and dispositions of practitioners. [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.]