The goal of this study is to understand the use of positive behavior support (PBS) practices, as well as factors that are associated with sustainable implementation of PBS practices in early care and education (ECE) programs in the state of Kansas. PBS practices can promote social emotional competence and reduce challenging behaviors in young children (Lucyshyn, Dunlap, & Freeman, 2015). As a result, national professional organizations (e.g., Division for Early Childhood, 2014) and federal and state regulatory agencies (e.g., U.S. Department of Health and Human Services & U.S. Department of Education, 2016) have promoted the implementation of PBS practices by the ECE workforce. However, there is a lack of knowledge on PBS professional development (PD) and implementation status at the program and state level. In addition, the field has limited understanding of real-world factors leading to PBS practice implementation and sustainability. Developing a deeper understanding of the factors that support implementation and sustainability as well as those that impede implementation and/or sustainability is crucial for ensuring that investments in professional development result in meaningful and sustained positive outcomes for young children and their families. Thus, the overarching goal of this dissertation is to expand the field’s knowledge of implementation of PBS practices at authentic ECE settings. The dissertation is grounded in an implementation science framework. A survey study was conducted to understand the current status of PBS PD and the level of implementation and sustainability of PBS practices in child care and Head Start programs in the state of Kansas. Policy and practice implications for supporting a sustainable professional development system to promote durable PBS implementation are addressed. (author abstract)