Over the past decade or so, the need for evidence-based programs has intensified from both research and policy perspectives. While much effort has been put into developing educational interventions and demonstrating their effectiveness, little work has been done to promote the sustained use of such evidence-based programs over time. Thus, this study examined the sustainability of Head Start REDI (Research-based, Developmentally Informed), an evidence-based preschool curriculum which combines pre-literacy components with a social-emotional learning (SEL) curriculum, by following the intervention teachers (N=21) for the first two years after the formal REDI randomized trial ended. A mixed methods framework that included qualitative interviews, teacher surveys, and classroom observations was used to explore the extent to which the components of the REDI curriculum are sustained and to identify the factors that facilitate and hinder sustainability. Results indicated that the REDI curriculum was sustained over time. PATHS, the SEL component, was sustained at the highest level with almost all teachers sustaining, while the pre-literacy components (Dialogic Reading, Sound Games and Alphabet Center) demonstrated somewhat lower rates of sustainability (approximately two-thirds of teachers). Barriers to sustainability of REDI included competition from other Head Start requirements, lack of time and teacher perceptions that REDI was not developmentally appropriate. Factors which facilitated sustainability included teacher perceptions of benefits to children, administrative mandates requiring REDI and teacher perceptions that the REDI approach matched her teaching style. Few pre-test factors were found to be associated with sustained use of REDI (e.g. teacher education and years experience or teacher characteristics). However, pre-REDI teaching quality was related to sustainability, as was implementation quality prior to the sustainability years. That REDI was sustained at all for the two years following the intervention year is encouraging given that sustained use of the curriculum was not one of the original goals of the Head Start REDI project. The discussion focuses on the implications of the findings for informing future efforts at fostering sustainability of evidence-based preschool curriculums, including the possibility that an administrative mandate may be needed to ensure sustainability. (author abstract)