The Partnership for Pre-K Improvement (PPI) was launched by the Bill & Melinda Gates Foundation in 2016 as a project with a vision to develop and sustain high-quality, equitable pre-K programs that produce improved and more-equitable kindergarten readiness and greater academic success for children through the early elementary grades. The multiyear, multistate effort aimed to learn in partnership with states across government leaders, advocates and researchers about how to systematically improve the quality of pre-K at scale. After five years of learning and implementation, PPI concluded in summer 2021 with key lessons to share with the field and a set of tools and resources for use by state leaders to advance quality and equity in pre-K systems. (author abstract)