Engagement in play has been definitively linked to the healthy development of children across physical, social, cognitive, and emotional domains. The enriched nature of high-quality outdoor play environments can afford a greater diversity of opportunities for play than indoor settings. To more effectively design outdoor play settings, we must better understand how the physical environment supports, or hinders, the different types of play which suit children’s needs and interests. However, play typologies or observation tools available to date do not adequately capture the unique characteristics of outdoor play. This paper outlines the development and testing of the Tool for Observing Play Outdoors (TOPO), a new typology of outdoor play, as well as a systematic field observational protocol which can be used to effectively depict children’s behaviors in outdoor spaces, as well as evaluate the play environment itself. The tool can be deployed in either a collapsed or expanded form to serve the needs of a wide range of studies and environments. This new tool represents a significant advance in the ability to fully and effectively study and plan outdoor play environments to provide more diverse, high-quality play settings that will support the healthy development of children across the spectrum.