Research Findings. Application of mixed methods in a dissemination and implementation framework can give researchers a better understanding of the reach and delivery of early childhood obesity prevention programs in preschool settings, as well as potential facilitators and barriers related to implementation and sustainability. This study utilized a simultaneous, exploratory, mixed-methods design to investigate individual-, organizational-, and intervention-level factors that were related to the implementation and sustainability of policy, system, and environment (PSE) changes as part of a larger obesity prevention program in a randomly selected sample of preschool centers (n = 20). Individual-level factors, and specifically the attitudes and skills of preschool providers, were identified in both the qualitative and quantitative data as important factors related to the sustainability of PSE changes (r = .56, p < .01). Staff and leadership engagement and adaptability of the program were also identified as important factors related to the implementation and sustainability of PSE changes. Practice or Policy. These findings highlight the complexity of implementation success and suggest PSE obesity prevention interventions in preschool centers require the consideration of numerous, multilevel factors to ensure programming is impactful and sustained over time. (author abstract)