High-quality pre-K sets children on a path to success in kindergarten and beyond. Yet most children in the United States do not attend high-quality programs, with particularly pronounced gaps in quality for children from families with low incomes, dual language learners, Black children, and Latino children. Ensuring equitable access to high-quality pre-K requires being able to measure quality, particularly at a large scale. This brief describes the existing landscape of widely used measures of pre-K quality, further spotlights some of the newer measurement work, and concludes with a discussion of future directions for the field.