Over the decades, counselors have been asked to provide culturally appropriate services to clients and make social justice efforts (American Counseling Association, 2014; Arredondo et al., 1996; Sue et al., 1982). School counselors have also been encouraged to act as social justice leaders who advocate for systemic changes in schools (Curry & DeVoss, 2009; Evans et al., 2011). The Association for Multicultural Counseling and Development (AMCD) commissioned a group of scholars to revise the original multicultural counseling competencies (Sue et al., 1992), which resulted in the development of the Multicultural and Social Justice Counseling Competencies (MSJCC) framework (Ratts et al., 2016). Although the MSJCC framework has been widely accepted in the field, to this day, measurements that were created based on this framework and tailored for school counseling are scarce. Consequently, the purpose of this study is to develop an instrument that measures school counselors' and trainees' self-evaluated multicultural and social justice counseling competencies. Accordingly, the instrument was named the Multicultural and Social Justice School Counseling Competencies Scale (MSJSCCS). Initial items of the MSJSCCS were created based on the MSJCC framework (Ratts et al., 2016), Ratts and Greenleaf's (2018) article, and ASCA School Counselor Professional Behavior Standards and Competencies (American School Counselor Association, 2019). Then, items were refined by conducting two rounds of content expert review and pretesting with a small number of people from the target population. After collecting data, 207 cases (45 school counseling master's students and 162 school counselors) were included in the data analysis. An exploratory factor analysis and an internal consistency reliability analysis were administered, and the relationships between the MSJSCCS and other constructs were explored. As a result, the MSJSCCS had a four-factor structure (Student Worldview, School Counseling and Advocacy Interventions, Counseling Relationship, and School Counselor Self-Awareness), which aligned with the domains in the MSJCC framework (Ratts et al., 2016). Cronbach's alpha reliability coefficients for subscales were either high or excellent (ranging from Cronbach's [alpha] = 0.838 to 0.912). Lastly, it was found that the MSJSCCS measured a similar construct with the Multicultural Counseling Competence and Training Survey--Revised (MCCTS-R; Holcomb-McCoy & Day-Vines, 2004) and a different construct with the Marlowe-Crowne Social Desirability Scale--Form C (Reynolds, 1982). Limitations and implications of this study, and recommendations for future research were further discussed. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]