Classroom observation measures that were originally developed and refined for early childhood research purposes are increasingly being used in state Quality Rating Systems (QRS), child care licensing, tiered reimbursement, and professional development. Understanding the characteristics and predictive power of these measures is critical to correctly interpreting and using the data that they produce. this brief reviews several widely used assessments and their relation to each other and to child outcomes. Particular attention is given to purposes for assessment, psychometric properties, inter-rater reliability, applicability of measures across ages, and content and cross-cultural validity. While several classroom observation methods have been shown to predict later child outcomes, classroom features and experiences still account for far less of child variability than family characteristics do. However, despite the modest sizes of the associations between child care quality and child outcomes, quality measures do consistently and significantly confirm these links; further development of quality measurement tools is warranted.