Good mentoring of graduate students influences their perseverance and success to completion, whereas bad mentoring can result in negative outcomes, including delayed degree completion or non-completion. What the authors refer to as the gray zone is that which falls between good and bad mentoring. Examples are partial mentoring or changes in mentoring needs that are not being met. First, the authors review the literature on good and bad mentoring, mentoring of specific demographic groups, and mentoring models. Second, they present interview results with 20 advanced science Ph.D. graduate students and recent graduates in the sciences, especially those results concerning the gray zone. Third, the authors make recommendations to improve mentoring and rectify problem areas in the gray zone.