Beginning in 2012, the foundation commissioned a series of research papers to better understand the changing early learning landscape. Specifically, these papers addressed whether pre-K programs produced gains in student achievement that persisted into the early elementary grades; whether high-quality programs could be cost sustainable; and what program features contribute to strong interactions between teachers and children, the central ingredient in high-quality programs. The result is the research presented here, along with a companion piece on the early childhood workforce. These three papers are based on published research, program evaluations, and extensive consultation with experts in the early childhood field. The research was iterative. As a result, conclusions about the components of high-quality--including the importance of B.A. degrees for lead teachers--evolved based on new information. The papers are presented sequentially to show the evolution of the project over approximately 18 months, and should be read together: Quality in Center-Based Early Learning: High-Level Findings and Trends (January 2013); Early Learning: The New Fact Base and Cost Sustainability (September 2013); and The Essential Elements of High-Quality Pre-K: An Analysis of Four Exemplar Programs (January 2014). (author abstract)