PROJECT SUMMARY/ABSTRACT The impact of poverty on child development is a critical public health issue. Nearly 1 billion children live below the poverty line worldwide. The early years of a child's life form the foundation for all later development. Investments in Integrated Early Childhood Development (ECD) programs are critical for breaking the intergenerational poverty cycle. Evidence is still lacking on how to implement and integrate ECD interventions in poverty setting where many competing priorities are in place. Specifically, it is unknown which pathways drive the implementation of ECD programs and whether integrating ECD program components into an existing national program targeting impoverished children can improve development outcomes. Recently, Brazil rolled out the Criana Feliz ECD program in response to the 2016 Brazilian National ECD legal framework This program focuses primarily on fostering nurturing care parenting skills to buffer the negative effects of poverty on children under 3 years and their families enrolled in Bolsa Famlia, the largest conditional cash transfer (CCT) program in the world. The Brazilian ECD and CCT programs lack integration. Filling in this gap is vital to improving ECD policies and initiatives embedded within existing programs targeting the most vulnerable children. This implementation science project takes a systems approach to achieve two goals: 1) identify pathways of implementation and bottlenecks of Criana Feliz, and 2) help optimize the impact of Bolsa Famlia on ECD outcomes through the integration of Criana Feliz with the food security components of the program. This project will use a mixed-methods approach grounded within a novel complex adaptive framework previously used for understanding the scaling up of breastfeeding and ECD programs in diverse countries but not in Brazil. Analyses will be based on the Program Impact Pathways process evaluation and a program optimization computational modelling approach informed by context and program specific data. Findings will be widely disseminated among decision makers in Brazil in conjunction with a policymaker toolbox to empower them to continue applying the optimization methodology in the future to continue improving ECD outcomes through Bolsa Famlia. Findings have great potential to be translated to other CCT programs worldwide. This proposal fits well with the candidate's long-term research interest to become an implementation science researcher in the field of ECD, specifically in program and policy evaluation. The completion of this project will provide data for a subsequent R01 grant application examining the impact of the optimized cost-effectiveness integration of food security and ECD programs to improve ECD outcomes under real-world conditions. Through this project the candidate will receive training in implementation science methods, health economics and ECD and will be able to transition to an independent academic position.