This report describes preliminary work in support of an early childhood needs assessment for American Indian and Alaska Native (AI/AN) children prenatal to age five. The report uses existing data to describe the population of AI/AN children and families and their participation in early childhood services. This work is part of a larger AI/AN Early Childhood Needs Assessment design project (AI/AN EC Needs Assessment), conducted for the Office of Planning, Research and Evaluation within the Administration for Children and Families, in the U.S. Department of Health and Human Services. Mathematica Policy Research convened a Community of Learning (CoL) to inform three design topics on describing the AI/AN population, studying early childhood services organization and delivery, and assessing features to support community capacity for conducting needs assessments, that form the basis for a needs assessment. For more information on the design topics see the design report (Malone et al. 2016). The current report presents the process and findings from implementing Design One--describing the population of AI/AN children and families and their participation in early childhood services based on existing data sources--with a set of national survey and ACF administrative data sources. Primary Research Questions The current implementation of Design One seeks to address three research questions: - What existing data sources could help us understand AI/AN early childhood needs? - What information from these sources has been published to date? - What can we learn about AI/AN early childhood needs when conducting new analyses by using existing sources? (author abstract)