Quality rating and improvement systems (QRISs) are designed to assess, improve, and communicate the quality of early care and education programs. Using administrative data, we investigated whether providers that participated in a county-level QRIS saw increases to their global quality (tier) rating, domain-specific quality ratings, and scores on an observation measure of classroom quality. Research Findings: On average, participating providers increased their overall tier ratings; this pattern was particularly true for providers with lower initial tier ratings. We found more consistent evidence of increases on indicators of structural quality components (e.g., teacher and director qualifications), and limited evidence of improvement on process quality indicators (e.g., measure of teacher-child interaction). This finding suggests structural quality improvements may be driving global tier rating changes. In addition, providers saw average increases on a measure of classroom quality, with larger increases seen in domains that measure classroom organization and emotional support. Practice and Policy: We discuss implications for how QRISs can promote quality improvement for participating providers and suggest avenues for future research.