Research Findings: A growing number of stakeholders in early childhood education (ECE) rely on self-assessment to assess and improve the quality of ECE. In this systematic review, we investigated the reliability and validity of self-assessment in ECE, summarizing findings from 27 publications. We meta-analytically synthesized findings from 25 publications for 1,882 groups and 79,163 children aged 0-72 months in center-based childcare. Most studies reported high internal consistency, but one study reported a lower consistency. Inter-rater reliability was generally high. A three-level meta-analysis (k = 13, ES = 45) revealed a positive association between self-assessment ratings and ratings with validated measures of ECE quality (r = 0.38), indicating a moderate convergent validity. Studies with lower methodological quality and published "peer reviewed" studies reported somewhat higher correlations between self-assessment ratings and ratings with validated measures. The meta-analytic correlation remained significant after removal of studies with lower methodological quality (r = 0.33) or studies from the "grey" literature (r = 0.44). A second meta-analysis (k = 16, ES = 71) with a focus on the predictive validity of self-assessment ratings showed a small significant association between self-assessed ECE quality and child outcomes (r = 0.09); there were no significant moderators. Practice or Policy: Despite empirical evidence for the validity of self-assessment, further studies are needed to investigate potential bias in self-assessment. Future studies should further explore the validity and reliability of self-assessment measures in ECE, including countries outside the United States.