The broad purpose of this study was to address gaps in the literature by applying the Relational Humility Model (RHM; Davis et al., 2010, 2011) to clinical supervision by testing the interpersonal variables of relational humility (RH; Davis et al., 2011), the supervisory working alliance (SWA, Bordin, 1983), and relational behavior (RB; Shaffer & Friedlander, 2017) as predictors of supervisee nondisclosure (SND; Ellis & Colvin, 2016; Siembor & Ellis, 2012), both clinically-related (CRND) and supervision-related (SRND). It was hypothesized that RH would moderate the relation between SWA and SRND and that the SWA would be a positive predictor of SND when controlling for RH and RB. It was further hypothesized that RB would be uniquely associated with SND. Participants were 312 trainees in the U.S. who predominately identified as White (73.6%), female (84.3%), doctoral students (86.1%) receiving clinical supervision across a range of practicum or internship settings. Collectively, the three predictors explained over a quarter (26%) of the variance in the multivariate construct of supervisee nondisclosure, such that the SWA uniquely predicted supervision-related and clinically-related nondisclosure but RB did not. RH significantly moderated the inverse relation between the SWA and supervision-related nondisclosure with an effect size of 5%. Results are discussed for their practical and theoretical implications, as well as limitations, and suggestions for future research. [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.]