ABSTRACT The overall goal of this K01 award is to support Dr. Long in becoming an independent investigator specializing in the use of cutting edge implementation methods to address health inequities and improve the health of birthing parents and infants. The focal point of the proposed research is to adapt an existing national breastfeeding program to improve breastfeeding initiation and duration in American Indian and Alaskan Native (AI/AN) communities. Breastfeeding provides enormous immediate and long-term health benefits for both infants and birthing people, reducing the risk of obesity, diabetes, and death in children, and cancer, diabetes, and cardiovascular diseases in birthing people. However, there are important racial and ethnic disparities in breastfeeding rates in the United States, and AI/AN communities are both less likely to breastfeed and are at greater risk for many of the adverse health outcomes that breastfeeding protects against. This proposed research will use methods grounded in community engagement and health equity to assess barriers to breastfeeding among AI/AN residents at the Lummi Indian Reservation, and then test adaptations designed to address those barriers and improve breastfeeding uptake and duration. The proposed work will use a novel optimization design that will allow for multiple strategies to be tested and will place priority on both efficacy and cost of program adaptations. The specific aims of this proposal are: 1) to assess barriers to breastfeeding in Lummi parents and identify adaptations to the existing promotion program to address those barriers; 2) to test adaptations to the program to identify an optimal adapted program; and 3) to determine acceptability, appropriateness, and feasibility of the adapted components. This proposed work has been designed to address a key public health priority identified by leadership at Lummi Tribal Health Center, and the work will be carried out in partnership with Lummi Tribal Health Center leaders and in collaboration with a community advisory board. These research aims are one aspect of a comprehensive training plan designed in coordination with an exemplary interdisciplinary mentorship team. Dr. Long will receive mentorship, training, and coursework in implementation science, community-based participatory research, and integration of health equity into research design. The specific training goals of this proposal include 1) gaining proficiency in the use of implementation science frameworks; 2) learning and applying advanced implementation science study designs; and 3) learning to conduct ethical equity-focused implementation research. The final goal is to provide Dr. Long with mentorship and support in career development, and this research and training plan will provide opportunities to publish original research, present at conferences and workshops, and gain visibility within her field. The resulting data from the proposed research will provide the basis for an R...