There is considerable concern regarding our nation's literacy skills. Research has repeatedly shown that the literacy trajectory is well established very early in the school career. Early childhood educators (ECEs) have the ability to influence a child's literacy skills provided they have the required knowledge and tools. Professional development (PD) is a means of providing the knowledge and skills, but is not always effective. This article presents the results of a systematic review of the literature of preschool children's phonological awareness improvement following PD for the respective ECEs. The results from 15 studies from 2003 to 2019 are synthesized and discussed to determine the components of PD that make it effective. The studies revealed a wide range of effect sizes, ranging from negligible to very large. Aspects of effective PD, including the education and experience of the ECEs, the format and structure of the PD, and the content of the educational program, are considered. The findings have important instructional implications for PD in the preschool setting.