As part of the Universal Preschool Child Outcomes Study (UPCOS-4), the authors are conducting a qualitative examination of quality support coaching in the Los Angeles Universal Preschool (LAUP) including an analysis of how coaching is being interpreted and implemented in the variety of contexts found in LAUP. This qualitative study will inform the design of a subsequent outcomes-focused study to be conducted in following years. Ultimately, LAUP leadership would like to be able to examine relationships between the coaching model and desired outcomes, such as classroom quality and child progress. An important step in this study is the review and examination of the existing literature on coaching, analysis of reviews that have been completed recently, and synthesis of what is known about coaching and its effectiveness. In this report, the authors identify studies that link coaching and specific coaching models with outcomes for classrooms, providers, and children, while also highlighting critical aspects of coaching. Specifically, they summarize the research base for coaching as a professional development tool, including the strengths and weaknesses of this research. In the appendix tables, the authors provide considerable detail to support the summary information in the body of the report. They begin by briefly describing the process of the literature review, including its sources of information.