This dissertation examines the role of the facilitator in elementary mathematics professional development. An exploratory sequential mixed methods design was utilized to answer the central research question: How do United States elementary school teachers perceive an influential facilitator of elementary mathematics professional development (EMPD)? Phase one of this study explored teacher perceptions through a phenomenological design, which informed the second phase of the study, the implementation of a survey instrument to elementary school mathematics teachers on a larger scale. This dissertation is divided into six chapters. Chapter One presents a rationale for examining the role of the facilitator in professional development. Chapter Two builds on this rationale by synthesizing and discussing the current literature relating to professional development. Chapter Three examines the procedures used in each phase of the mixed methods research design. Within this examination are the specific sampling, data collection, and data analysis procedures that were used to investigate the central research question. Chapters Four and Five present the results of each phase of the research design and Chapter Six provides a discussion of these results with implications for future research.