High-quality supervision for teachers in early care and education (ECE) is essential for building positive teacher-child relationships and enhancing ECE program quality, which in turn promotes healthy social-emotional and academic development in young children. Reflective supervision (RS) is a process-oriented and relationship-centered supervisory approach that has growing empirical evidence supporting its use. As the evidence base for RS continues to expand, and early childhood-serving settings--including ECE--increasingly consider this approach, understanding whether RS is likely to be routinely used in ECE settings and what helps or hinders use of this approach is critically important. Thus, the aims of this study were to assess the feasibility, acceptability, and appropriateness of RS in state-funded pre-Kindergarten (state pre-K) programs, as well as delineate the implementation determinants that either advanced or challenged the use of RS in state pre-K. This study was informed and guided by the updated Consolidated Framework for Implementation Research (CFIR) and the CFIR Outcomes Addendum. Participants included 11 state pre-K program supervisors who had been trained in RS. Participants completed brief measures of feasibility, acceptability, and appropriateness of RS, and semi-structured interviews. Descriptive analyses of quantitative measures revealed that participants perceived RS as feasible to implement in their programs, highly acceptable, and highly appropriate, thereby suggesting that RS is likely to be implemented successfully in this setting. Qualitative data obtained from interviews and coded using the updated CFIR lent greater nuance to these results by specifying the facilitators and barriers affecting implementation. All participants reported great need for RS at the supervisor, teacher, and child/family level, and identified numerous other facilitating factors within four CFIR domains (i.e., "Innovation, Outer Setting, Inner Setting," and "Individuals"), ranging from the relative advantage of RS to individual supervisor motivation and capability. Participants also cited barriers to using RS, most notably staffing difficulties, competing demands, and lack of policy and leadership support. Through theory-driven implementation frameworks applied to a real-world ECE setting, these findings extend prior research suggesting that RS may be an effective supervisory approach by highlighting the contextual factors that make RS more or less likely to be adopted, used, and sustained in state pre-K.