High-quality care in the earliest years of life has been shown to relate to positive developmental outcomes for children, including improved early academic skills, social-emotional competencies, and cognitive functioning. Unfortunately, the early care experiences of many children are not always high quality; rather, research suggests that high-quality care is the exception. The growing evidence relating quality care to improved outcomes, the variability in quality across care settings, and the failure of existing approaches to improve child care have led to a national call to enhance the quality of early care and education programs. In response to this call, states have created "Quality Rating and Improvement Systems" (QRISs). The ultimate goal of a state QRIS is to assist service providers in the delivery of quality early care and education in order to improve children's developmental outcomes. Pennsylvania's QRIS, Keystone STARS, was one of the first systems in the nation. A team from the University of Pennsylvania was funded by the William Penn Foundation to conduct an inquiry of "Keystone STARS." The goal of this inquiry was to provide a broad look at Keystone STARS to inform future revisions and evaluation of the system as part of Pennsylvania's Race to the Top Early Learning Challenge grant (2013-2018). The inquiry focused on providing an overarching look at Keystone STARS with respect to three major areas: (1) "Child outcomes": Examined the relations between Keystone STARS and children's overall developmental competencies; (2) "Quality components": Inquiry investigated the extent of evidence from theory, empirical research, and practitioner expertise linking each of the Keystone STARS quality components to child outcomes; and (3) "Systems approach to rating quality and guiding improvements": Examined overall features of the system that could be improved to enhance the effectiveness and efficiency of the system. The research report presents a detailed review of the data and findings for each of the three aspects of the inquiry. The report concludes with an overview of the lessons learned and points to promising areas of reform for improving Keystone STARS for the children of Pennsylvania. The following are appended: (1) Examination of WSS, (2) Provider Survey, (3) STARS interview protocol, and (4) Logic models.