Arizona's First Things First partners with other agencies to create a high-quality, family-centered, comprehensive, and collaborative early childhood system that supports the development, health, and early education of all Arizona's children through age 5, helping ensure they enter kindergarten healthy and ready to succeed. One of First Things First's strategies is Quality First, a voluntary Quality Improvement and Rating System. Quality First partners with child care and preschool providers to improve the quality of early learning across Arizona. The system assesses providers on evidence-based indicators of quality, funds supports to help providers enhance program quality, and publicly rates providers. Quality First offers five quality improvement services to participating early care and education programs: (1) Coaching; (2) Assessment; (3) Financial incentives; (4) Specialized assistance; and (5) Professional development. In September 2015, First Things First contracted with Child Trends, a national research organization, to evaluate Quality First in order to inform implementation and continuous improvement of the initiative. The study used mixed methods including surveys of stakeholders and participants, observations of program quality, focus groups, interviews, and document review. Findings recommend ways to increase access to more specialized technical assistance and provide additional training or professional development to participants on how to better interpret and use assessment results. Results note opportunities to strengthen Quality First's engagement and outreach to providers to support program participation. While data collection methods are thorough and strong, Quality First should provide more technical assistance to stakeholders about why certain data are being collected and how it is used. The validation study findings do not suggest major changes are needed to the Quality First rating scale, as it is functioning as expected in differentiating levels of quality. There is, however, a need for additional quality improvement efforts to support Quality First participants in continuing to achieve higher ratings. [First Things First (also known as the Arizona Early Childhood Development and Health Board) and the First Things First Research and National Advisory Panel participated in presentations of findings and input on drafts of this report. The project was supported by Arizona's First Things First initiative.]