The aspiration of the LEGO Foundation is to support children to become creative, engaged, lifelong learners, who thrive in a constantly changing world by experiencing the benefits of learning through play. Learning through play offers deep learning experiences that are joyful, meaningful, active, engaged, iterative, and social. Effective teacher professional development (TPD) is a critical component of any effort to bring learning through play into more classrooms. The LEGO Foundation funded Education Development Center (EDC) to conduct foundational research on the elements of effective TPD, approaches to measuring teacher and student outcomes related to learning through play, and the conditions that enable and support teacher implementation of learning through play pedagogies, with specific attention paid to research on and conditions of TPD in the United States. This summary report brings together a review of existing research, exploration of existing programs, and interviews with teachers to illuminate the potential of TPD to support learning through play as well as the challenges present in this work.