Quality Rating Improvement Systems (QRIS) are now operating state-wide in 18 states. An additional 13 states are implementing QRIS in selected regions or as pilot initiatives. While highly varied in their specific features, these systems all use a set of interrelated strategies that aim to raise the quality of early care and education programs. These strategies include quality standards that programs must meet to obtain ratings at different levels, financial incentives for programs to meet quality standards, and assistance to help center-based programs and home-based providers improve the quality of supports for children's well-being and early learning. As these systems increase in number across the states, ongoing examination of their characteristics and impacts can inform efforts to strengthen them. This report presents findings from an interview study that investigated features of the professional development and on-site assistance available to center-based staff and home-based providers who participate in states' Quality Rating Improvement Systems. The report's five sections address the following topics: (1) Rational for the study and research that helped frame the project; (2) Project overview and methods; (3) Key findings: (a) Supports used during the "entry phase"; (b) Availability and targeting of on-site assistance; (c) Features of on-site assistance; (d) Features of group training; and (e) Credentials and support of trainers and technical assistance providers; (4) Summary of findings; and (5) Recommendations.