Research Findings: The goal of this study was to examine empirical research on the design, delivery, and measurement of the effects of professional development (PD) for early childhood educators in order to provide insight into what the field has accomplished as well as suggest directions for future PD programs and research. Through the use of rigorous inclusion criteria outlined by S. M. Wilson, R. E. Floden, and J. Ferrini-Mundy (2001), 73 studies were included and analyzed. On average, 25% (M ¼ 12.68, SD ¼ 9.99) of references in each study were specifically about PD. The majority of studies (n ¼ 39) targeted some form of language and literacy instruction, whereas only 5 studies targeted math and 1 study targeted science. A total of 35 different delivery mechanisms were used to provide PD, with 40 studies including some form of coaching and 45 including training workshops. The studies used a wide range of methods to measure PD-related outcomes: 51% (n ¼ 37) of studies examined changes in teacher practice, 18% (n ¼ 13) measured changes in teachers' knowledge, 40% (n ¼ 29) measured changes in children's learning, and 11% (n ¼ 8) measured changes in children's behavior. Practice or Policy: Based on the results of this study, there are 4 major ways in which PD for early childhood educators can be developed. Researchers and providers of PD should (a) continue to draw from multiple resources to inform PD implementation designs, (b) include more diversity in the content of instruction targeted by PD, (c) experiment with innovative formats for delivering PD, and (d) create better means of evaluating PD.There is growing consensus that professional development (PD) is an especially important lever for improving teaching practice in early childhood education (ECE). Teachers' experiences with PD have been linked to higher classroom quality (Burchinal, Cryer, Clifford, & Howes, 2002), and some researchers suggest that PD might be the most impactful way of improving children's learning above and beyond teacher degree attainment or specific curriculum selection (e.g., Early et al., 2007; Preschool Curriculum Evaluation Research Consortium, 2008). Given the importance of PD for improving instruction in ECE, the field needs a better conception of what researchers are currently doing with PD in order to understand the growing knowledge base and find gaps in knowledge that need to be addressed. To that end, the present study systematically examined empirical research on the design, delivery, and reported measurement of the effects of PD for teachers of young children in order to provide insight into what the field has done as well as suggest directions for future PD programs and research.