Despite the widely shared assumption that public participation impacts planning implementation, empirical research rarely tests this belief. By reviewing what is known about if and how public participation impacts plan and planning implementation, and why we know so little, this review identifies a significant gap in the planning literature. The article synthesizes public participation and planning implementation literature to explain why this gap exists. This review is focused on one central research question: why is our empirical understanding of the overlap between public participation and implementation so limited? Building from these limitations, the article concludes with suggested directions for future research.