Children living in situations affected by conflict experience multiple adversities including exposure to violence, displacement, and family separation and can experience high levels of stress and insecurity. In order to bolster the case for interventions focused on young children in conflict-affected settings, this dissertation focuses on implementation research for early childhood development programming in humanitarian settings. With a clear focus on this overarching theme, this dissertation includes three connected, yet distinct papers in Chapters 2, 3, and 4. Chapter 2 presents a literature review of empirical research of early childhood development programs in humanitarian settings and draws from existing theories to present a framework for early childhood development implementation research in humanitarian settings. Chapters 3 and 4 focus on a specific example of the implementation of an ECD program in a humanitarian setting: Lebanon’s Preschool Healing Classroom (PHC) program. Chapter 3 includes an analysis of children’s developmental growth over the course of the PHC program using the International Development and Early Learning Assessment (IDELA); an exploration of the associations between demographic characteristics and IDELA scores; a psychometric analysis of an adaptation of the Monitoring Early Learning Environments (MELE) through exploratory factor analysis; and a multi-level analysis of the associations between the empirically obtained factors of classroom quality and children’s development. Using a concurrent mixed-methods approach, chapter 4 extends the findings reported in Chapter 3 and focuses on the factors affecting access and quality implementation that may influence children’s learning outcomes through the analysis of the perspectives of parents, Lebanese teachers, Syrian facilitators and Lebanese staff. The emergent themes are then integrated with a quantitative analysis of performance scores for each of the locations included in the qualitative study to shed light on potential influences of children’s developmental outcomes that were not previously captured in quantitative analysis presented in Chapter 3. In sum, this dissertation provides important insights for practitioners, researchers, and donor institutions looking to change the trajectory and enhance the lives of young children and families living in situations of conflict and crisis.